Reactors and systems for oxidative coupling of methane

ABSTRACT

In an aspect, the present disclosure provides a method for the oxidative coupling of methane to generate hydrocarbon compounds containing at least two carbon atoms (C 2+  compounds). The method can include mixing a first gas stream comprising methane with a second gas stream comprising oxygen to form a third gas stream comprising methane and oxygen and performing an oxidative coupling of methane (OCM) reaction using the third gas stream to produce a product stream comprising one or more C 2+  compounds.

CROSS-REFERENCE

This application is a continuation of U.S. patent application Ser. No.16/035,311, filed Jul. 13, 2018, which is a continuation of U.S. patentapplication Ser. No. 14/553,795, filed Nov. 25, 2014, now U.S. Pat. No.10,047,020, which claims priority to U.S. Provisional Patent ApplicationNo. 61/909,955, filed Nov. 27, 2013, and U.S. Provisional PatentApplication No. 61/909,980, filed Nov. 27, 2013, each of which isentirely incorporated herein by reference.

BACKGROUND

The modern petrochemical industry makes extensive use of cracking andfractionation technology to produce and separate various desirablecompounds from crude oil. Cracking and fractionation operations areenergy intensive and generate considerable quantities of greenhousegases.

The gradual depletion of worldwide petroleum reserves and thecommensurate increase in petroleum prices may place extraordinarypressure on refiners to minimize losses and improve efficiency whenproducing products from existing feedstocks, and also to seek viablealternative feedstocks capable of providing affordable hydrocarbonintermediates and liquid fuels to downstream consumers.

Methane may provide an attractive alternative feedstock for theproduction of hydrocarbon intermediates and liquid fuels due to itswidespread availability and relatively low cost when compared to crudeoil. Worldwide methane reserves may be in the hundreds of years atcurrent consumption rates and new production stimulation technologiesmay make formerly unattractive methane deposits commercially viable.

Ethylene is an important commodity chemical intermediate. It may be usedin the production of polyethylene plastics, polyvinyl chloride, ethyleneoxide, ethylene chloride, ethylbenzene, alpha-olefins, linear alcohols,vinyl acetate, and fuel blendstocks such as, but not limited to,aromatics, alkanes, and alkenes. With economic growth in developed anddeveloping portions of the world, demand for ethylene and ethylene basedderivatives continues to increase. Currently, ethylene is producedthrough the cracking of ethane derived either from crude oildistillates, called naphtha, or from the relatively minor ethanecomponent of natural gas. Ethylene production is primarily limited tohigh volume production as a commodity chemical in relatively large steamcrackers or other petrochemical complexes that also process the largenumber of other hydrocarbon byproducts generated in the crude oilcracking process. Producing ethylene from far more abundant andsignificantly less expensive methane in natural gas provides anattractive alternative to ethylene derived from ethane in natural gas orcrude oil. Oligomerization processes can be used to further convertethylene into longer chain hydrocarbons useful as polymer components forplastics, vinyls, and other high value polymeric products. Additionally,these oligomerization processes may be used to convert ethylene to otherlonger hydrocarbons, such as C₆, C₇, C₈ and longer hydrocarbons usefulfor fuels like gasoline, diesel, jet fuel and blendstocks for thesefuels, as well as other high value specialty chemicals.

SUMMARY

Recognized herein is the need for systems and methods for convertingmethane to higher chain hydrocarbons, such as hydrocarbon compounds withtwo or more carbon atoms (also “C₂₊ compounds” herein), in an efficientand/or commercially viable process. An oxidative coupling of methane(“OCM”) reaction is a process by which methane can form one or more C₂₊compounds.

The present disclosure provides reactors, systems and methods that canbe used to react methane in an OCM process to yield products comprisingC₂₊ compounds. OCM reactors, systems and methods of the presentdisclosure can be integrated in various hydrocarbon processes. Theefficient and/or commercially viable formation of C₂₊ compounds frommethane can be influenced by a number of different parameters that canboth affect the progress of the overall reaction of methane to ethylene,as well as provide opportunities for efficiency outside of the reactionprogress, e.g., through energy efficient processes and systems,recycling opportunities and the like.

An aspect of the present disclosure provides a method for the oxidativecoupling of methane to generate hydrocarbon compounds containing atleast two carbon atoms (C₂₊ compounds), comprising: (a) mixing a firstgas stream comprising methane with a second gas stream comprising oxygento form a third gas stream comprising methane and oxygen, wherein (i)the temperature variation of said third gas stream is less than about10° C., (ii) the variation of the concentration of methane to theconcentration of oxygen (CH₄/O₂) in said third gas stream is less thanabout 10%, and/or (iii) the variation of the flow rate of said third gasstream is less than about 5%; and (b) performing an oxidative couplingof methane (OCM) reaction using said third gas stream to produce aproduct stream comprising one or more C₂₊ compounds.

In some embodiments of aspects provided herein, the method furthercomprises separating said product stream into at least a fourth streamand a fifth stream, wherein said fourth stream has a lower C₂₊concentration than said fifth stream, wherein said fifth stream has ahigher C₂₊ concentration than said product stream. In some embodimentsof aspects provided herein, (a) comprises any two of (i)-(iii). In someembodiments of aspects provided herein, wherein (a) comprises (i), (ii)and (iii).

An aspect of the present disclosure provides a method for the oxidativecoupling of methane to generate hydrocarbon compounds containing atleast two carbon atoms (C₂₊ compounds), comprising: (a) in a mixer,mixing a first gas stream comprising methane with a second gas streamcomprising oxygen to form a third gas stream comprising methane andoxygen, wherein said third gas stream has a composition that is selectedsuch that at most 5% of said oxygen in said third gas streamauto-ignites; and (b) performing an oxidative coupling of methane (OCM)reaction using said third gas stream to produce a product streamcomprising one or more C₂₊ compounds.

In some embodiments of aspects provided herein, the method furthercomprises separating said product stream into at least a fourth streamand a fifth stream, wherein said fourth stream has a lower C₂₊concentration than said fifth stream, wherein said fifth stream has ahigher C₂₊ concentration than said product stream. In some embodimentsof aspects provided herein, the composition of said third gas stream isselected such that at most 1% of said oxygen in said third gas streamauto-ignites. In some embodiments of aspects provided herein, thecomposition of said third gas stream is selected such that at most 0.1%of said oxygen in said third gas stream auto-ignites. In someembodiments of aspects provided herein, the composition of said thirdgas stream is selected such that substantially no oxygen in said thirdgas stream auto-ignites. In some embodiments of aspects provided herein,said mixer comprises one or more airfoil-shaped manifolds.

An aspect of the present disclosure provides a method for the oxidativecoupling of methane to generate hydrocarbon compounds containing atleast two carbon atoms (C₂₊ compounds), comprising: (a) in a mixer,mixing a first gas stream comprising methane with a second gas streamcomprising oxygen to form a third gas stream comprising methane andoxygen, wherein said third gas stream has a substantially non-symmetricdistribution of residence times along a direction of flow of said thirdstream; and (b) performing an oxidative coupling of methane (OCM)reaction using said third gas stream to produce a product streamcomprising one or more C₂₊ compounds.

In some embodiments of aspects provided herein, the method furthercomprises separating said product stream into at least a fourth streamand a fifth stream, wherein said fourth stream has a lower C₂₊concentration than said fifth stream, wherein said fifth stream has ahigher C₂₊ concentration than said product stream. In some embodimentsof aspects provided herein, said OCM reaction is performed in an OCMreactor downstream of said mixer. In some embodiments of aspectsprovided herein, at least a portion of said OCM reaction is performed insaid mixer. In some embodiments of aspects provided herein, saiddistribution of residence times is selected such that greater than 95%of said third stream spends less than an auto-ignition delay time insaid mixer. In some embodiments of aspects provided herein, saiddistribution of residence times is selected such that greater than 99%of said third stream spends less than an auto-ignition delay time insaid mixer. In some embodiments of aspects provided herein, saiddistribution of residence times is selected such that greater than 99.9%of said third stream spends less than an auto-ignition delay time insaid mixer. In some embodiments of aspects provided herein, said mixercomprises one or more airfoil-shaped manifolds.

An aspect of the present disclosure provides a method for the oxidativecoupling of methane to generate hydrocarbon compounds containing atleast two carbon atoms (C₂₊ compounds), the method comprising: (a) in amixer, mixing a first gas stream comprising methane with a second gasstream comprising oxygen to form a third gas stream comprising methaneand oxygen; and (b) within a time period less than an auto-ignitiondelay time of oxygen and methane in said third gas stream, performing anoxidative coupling of methane (OCM) reaction using said third gas streamto produce a product stream comprising one or more C₂₊ compounds.

In some embodiments of aspects provided herein, the method furthercomprises separating said product stream into at least a fourth streamand a fifth stream, wherein said fourth stream has a lower C₂₊concentration than said fifth stream, wherein said fifth stream has ahigher C₂₊ concentration than said product stream. In some embodimentsof aspects provided herein, said auto-ignition delay time is from about20 milliseconds (ms) to 500 ms at a pressure from about 1 bar (absolute)and 30 bars and a temperature from about 400° C. and 750° C. In someembodiments of aspects provided herein, said mixer comprises one or moreairfoil-shaped manifolds.

An aspect of the present disclosure provides a method for the oxidativecoupling of methane to generate hydrocarbon compounds containing atleast two carbon atoms (C₂₊ compounds), the method comprising: (a) in amixer, mixing a first gas stream comprising methane with a second gasstream comprising oxygen to form a third gas stream comprising methaneand oxygen, wherein upon said mixing, flow separation does not occurbetween said mixer and said first gas stream, said second gas stream,and/or said third gas stream; and (b) performing an oxidative couplingof methane (OCM) reaction using said third gas stream to produce aproduct stream comprising one or more C₂₊ compounds.

In some embodiments of aspects provided herein, the method furthercomprises separating said product stream into at least a fourth streamand a fifth stream, wherein said fourth stream has a lower C₂₊concentration than said fifth stream, wherein said fifth stream has ahigher C₂₊ concentration than said product stream. In some embodimentsof aspects provided herein, said mixer comprises one or moreairfoil-shaped manifolds.

An aspect of the present disclosure provides a method for flame-lessauto-thermal reforming (ATR) to generate syngas, the method comprising:(a) mixing a first gas stream comprising methane with a second gasstream comprising oxygen to form a third gas stream; and (b) prior toauto-ignition of said third gas stream, performing a flame-lessauto-thermal reforming (ATR) reaction using said third gas stream toproduce a product stream comprising hydrogen (H₂) and carbon monoxide(CO).

An aspect of the present disclosure provides a system for mixing two ormore gas streams, comprising: (a) a conduit comprising a fluid flow pathfor a first gas; (b) a plurality of airfoil-shaped manifolds distributedacross said fluid flow path, wherein each of said airfoil-shapedmanifolds comprises one or more openings that inject a second gas intosaid fluid flow path such that said first gas and second gas becomeuniformly mixed; and (c) a reactor bed in fluid communication with saidfluid flow path, wherein said reactor bed comprises an oxidativecoupling of methane catalyst.

In some embodiments of aspects provided herein, said manifolds preventflow separation within said mixer. In some embodiments of aspectsprovided herein, said manifolds mix said first gas and said second gaswithin about 200 milliseconds. In some embodiments of aspects providedherein, said reactor bed is in contact with at least a portion of saidmanifolds. In some embodiments of aspects provided herein, each of saidairfoil-shaped manifolds comprises a first end and a second end situatedalong said fluid flow path, wherein said one or more openings aredisposed between said first end and said second end.

An aspect of the present disclosure provides a reactor system forperforming oxidative coupling of methane to generate hydrocarboncompounds containing at least two carbon atoms (C₂₊ compounds),comprising: (a) a mixer comprising (i) a conduit providing a fluid flowpath for a first gas stream comprising methane and (ii) a plurality ofairfoil-shaped manifolds distributed across said fluid flow path,wherein said airfoil-shaped manifolds inject a second gas streamcomprising oxygen into said fluid flow path to provide a third gasstream comprising methane and oxygen; and (b) a catalyst that performsan oxidative coupling of methane (OCM) reaction using said third gasstream to produce a product stream comprising one or more C₂₊ compounds.

In some embodiments of aspects provided herein, said airfoil-shapedmanifolds are in contact with said catalyst. In some embodiments ofaspects provided herein, said reactor comprises at least two stages ofmixer and catalyst. In some embodiments of aspects provided herein, saidreactor comprises a bypass leg directing a portion of said first gasstream to a mixer stage located after a first catalyst stage and beforea second catalyst stage. In some embodiments of aspects provided herein,said reactor comprises an internal heat exchanger that is capable oftransferring heat from said catalyst to said second gas stream prior tosaid second gas stream entering said mixer. In some embodiments ofaspects provided herein, said airfoil-shaped manifolds uniformly mixsaid first and second gas streams to provide said third gas stream. Insome embodiments of aspects provided herein, said catalyst is includedin a catalyst bed. In some embodiments of aspects provided herein, atleast a portion of said catalyst bed is in said mixer. In someembodiments of aspects provided herein, said catalyst bed is in areactor downstream of said mixer.

An aspect of the present disclosure provides a reactor system forperforming oxidative coupling of methane to generate hydrocarboncompounds containing at least two carbon atoms (C₂₊ compounds),comprising: (a) a mixer capable of mixing a first gas stream comprisingmethane with a second gas stream comprising oxygen to provide a thirdgas stream; (b) a catalyst that performs an oxidative coupling ofmethane (OCM) reaction using said third gas stream to produce a productstream comprising one or more C₂₊ compounds, wherein said OCM reactionliberates heat; and (c) one or more flow reversal pipes in fluidcommunication with said mixer and at least partially surrounded by saidcatalyst, wherein said flow reversal pipes comprise an inner pipecircumscribed by an outer pipe along at least a portion of the length ofsaid inner pipe, wherein said inner pipe is open at both ends and saidouter pipe is closed at an end that is surrounded by said catalyst,wherein said flow reversal pipes are configured to transfer heat fromsaid catalyst to said second gas stream during flow along said innerpipe and/or a space between said inner pipe and outer pipe.

In some embodiments of aspects provided herein, said second gas stream(i) flows through said inner pipe into said catalyst along a firstdirection and (ii) flows in a space between said inner pipe and outerpipe out of said catalyst along a second direction that is substantiallyopposite to said first direction. In some embodiments of aspectsprovided herein, said second gas stream (i) flows through a spacebetween said inner pipe and outer pipe and into said catalyst along afirst direction and (ii) flows in said inner pipe and out of saidcatalyst along a second direction that is substantially opposite to saidfirst direction.

An aspect of the present disclosure provides a system for performingoxidative coupling of methane (OCM) reaction to generate hydrocarboncompounds containing at least two carbon atoms (C₂₊ compounds),comprising: (a) an OCM reactor comprising an OCM catalyst thatfacilitates an OCM reaction to generate said C₂₊ compounds; (b) aninjector comprising a fluid flow conduit that directs a first gas streamthrough at least a portion of said OCM reactor to one or more openingsthat are in fluid communication with said OCM reactor, wherein saidfluid flow conduit is in thermal communication with said OCM reactor,and wherein said first gas stream comprises one of methane and anoxidizing agent; and (c) a gas distribution manifold comprising one ormore openings that are in fluid communication with said one or moreopenings of said injector and said OCM reactor, wherein said gasdistribution manifold directs a second gas stream into said OCM reactor,which second gas stream comprises the other of methane and saidoxidizing agent.

In some embodiments of aspects provided herein, said oxidizing agentcomprises O₂. In some embodiments of aspects provided herein, saidinjector comprises one or more ribs each comprising one or moreopenings. In some embodiments of aspects provided herein, said one ormore ribs are airfoils.

An aspect of the present disclosure provides a method for performingoxidative coupling of methane (OCM) reaction to generate hydrocarboncompounds containing at least two carbon atoms (C₂₊ compounds),comprising: (a) directing a first stream comprising methane and a secondstream comprising an oxidizing agent to an OCM reactor comprising an OCMcatalyst that facilitates an OCM reaction to generate said C₂₊compounds, wherein at least a portion of said first stream and/or secondstream is in thermal communication with said OCM reactor; (b) performingan OCM reaction using said methane and oxidizing agent to generate saidC₂₊ compounds and heat; and (c) directing at least a portion of saidheat to said first stream and/or said second stream.

In some embodiments of aspects provided herein, said oxidizing agentcomprises O₂. In some embodiments of aspects provided herein, said firststream is directed through said OCM reactor. In some embodiments ofaspects provided herein, said second stream is directed through said OCMreactor.

An aspect of the present disclosure provides a method for producing atleast one C₂₊ alkene, comprising: (a) directing methane and an oxidizingagent into a reactor comprising a catalyst unit and a cracking unitdownstream of said catalyst unit, wherein said catalyst unit comprisesan oxidative coupling of methane (OCM) catalyst that facilitates an OCMreaction, and wherein said cracking unit generates C₂₊ alkene from C₂₊alkane; (b) reacting said methane and oxidizing agent with the aid ofsaid OCM catalyst to generate at least one OCM product comprising atleast one C₂₊ compound; (c) providing at least one OCM product in ahydrocarbon-containing stream that is directed through said crackingunit, which hydrocarbon-containing stream comprises at least one C₂₊alkane; and (d) in said cracking unit, cracking said at least one C₂₊alkane to provide said at least one C₂₊ alkene in a product stream thatis directed out of said reactor, wherein said cracking unit is operatedat a (i) hydrocarbon-containing stream residence time and (ii) crackingunit temperature profile selected such that the ratio of C₂₊ alkene toC₂₊ alkane in said product stream is greater than 0.1.

In some embodiments of aspects provided herein, said OCM catalyst is ananowire catalyst. In some embodiments of aspects provided herein, saidoxidizing agent is O₂. In some embodiments of aspects provided herein,said at least one C₂₊ compound comprises said C₂₊ alkane. In someembodiments of aspects provided herein, in (c), said C₂₊ alkane isprovided from a source external to said reactor. In some embodiments ofaspects provided herein, said source is a natural gas liquids source. Insome embodiments of aspects provided herein, said at least one C₂₊alkane comprises a plurality of C₂₊ alkanes. In some embodiments ofaspects provided herein, said plurality of C₂₊ alkanes are each directedinto said cracking unit at different locations. In some embodiments ofaspects provided herein, said cracking unit generates C₂₊ alkene fromC₂₊ alkane with the aid of heat generated in said OCM reaction. In someembodiments of aspects provided herein, said generating of (d) isadiabatic. In some embodiments of aspects provided herein, saidhydrocarbon-containing stream is directed through said cracking unit ata residence time that is less than or equal to 1 second. In someembodiments of aspects provided herein, said residence time is less thanor equal to 500 milliseconds. In some embodiments of aspects providedherein, said temperature profile is from about 750° C. to 950° C. Insome embodiments of aspects provided herein, said cracking unit has aninlet and an outlet downstream of said inlet, where saidhydrocarbon-containing stream is directed from said inlet to saidoutlet, and wherein said inlet is at a temperature from about 880° C. to950° C. and said outlet is at a temperature from about 750° C. to 880°C. In some embodiments of aspects provided herein, said ratio is greaterthan 1. In some embodiments of aspects provided herein, said ratio isgreater than 3. In some embodiments of aspects provided herein, saidratio is greater than 5.

An aspect of the present disclosure provides a method for producing atleast one C₂₊ alkene, comprising: (a) directing methane and an oxidizingagent into a reactor comprising a catalyst unit and a cracking unitdownstream of said catalyst unit, wherein said catalyst unit comprisesan oxidative coupling of methane (OCM) catalyst that facilitates an OCMreaction, and wherein said cracking unit generates C₂₊ alkene from C₂₊alkane; (b) reacting said methane and oxidizing agent with the aid ofsaid OCM catalyst to generate at least one OCM product comprising atleast one C₂₊ compound; (c) providing at least one OCM product in ahydrocarbon-containing stream that is directed through said crackingunit from an inlet to an outlet at a residence time that is less than500 milliseconds at a reactor diameter of at least about 12 inches,wherein said inlet is at a temperature from about 800° C. to 950° C. andsaid outlet is at a temperature from about 700° C. to 950° C., andwherein said hydrocarbon-containing stream comprises at least one C₂₊alkane; and (d) in said cracking unit, cracking said at least one C₂₊alkane to provide said at least one C₂₊ alkene in a product stream thatis directed out of said reactor.

In some embodiments of aspects provided herein, said OCM catalyst is ananowire catalyst. In some embodiments of aspects provided herein, saidoxidizing agent is O₂. In some embodiments of aspects provided herein,said at least one C₂₊ compound comprises said C₂₊ alkane. In someembodiments of aspects provided herein, in (c), said C₂₊ alkane isprovided from a source external to said reactor. In some embodiments ofaspects provided herein, said source is a natural gas liquids source. Insome embodiments of aspects provided herein, said at least one C₂₊alkane comprises a plurality of C₂₊ alkanes. In some embodiments ofaspects provided herein, said plurality of C₂₊ alkanes are each directedinto said cracking unit at different locations. In some embodiments ofaspects provided herein, said different locations are locatedsequentially along said cracking unit's length based on a carbon numberof said plurality of C₂₊ alkanes directed thereto. In some embodimentsof aspects provided herein, said cracking unit generates C₂₊ alkene fromC₂₊ alkane with the aid of heat generated in said OCM reaction. In someembodiments of aspects provided herein, said residence time is less thanor equal to 200 milliseconds. In some embodiments of aspects providedherein, said catalyst unit comprises a packed bed catalyst. In someembodiments of aspects provided herein, said diameter is greater than orequal to about 10 feet. In some embodiments of aspects provided herein,said diameter is greater than or equal to about 15 feet.

An aspect of the present disclosure provides an oxidative coupling ofmethane (OCM) system, comprising: (a) a catalyst unit comprising an OCMcatalyst that facilitates the reaction of methane and an oxidizing agentin an OCM reaction to generate an OCM product comprising at least oneC₂₊ compound; (b) a cracking unit downstream of said catalyst unit,wherein said cracking unit accepts said OCM product in ahydrocarbon-containing stream that is directed from an inlet to anoutlet of said cracking unit, and wherein said cracking unit generatesat least one C₂₊ alkene from at least one C₂₊ alkane in saidhydrocarbon-containing stream; and (c) one or more inputs to saidcracking unit, wherein a given input among said one or more inputs is influid communication with said hydrocarbon-containing stream, and whereinsaid given input provides one or more C₂₊ alkanes to said cracking unit.

In some embodiments of aspects provided herein, said catalyst unitcomprises a packed bed. In some embodiments of aspects provided herein,said one or more inputs comprise a plurality of inputs. In someembodiments of aspects provided herein, said plurality of inputscomprises a first input for a first alkane and a second input for asecond alkane, wherein said first alkane has fewer carbon atoms thansaid second alkane, and wherein said first input is closer to said inletthan said second input. In some embodiments of aspects provided herein,said one or more alkanes are selected from the group consisting ofethane, propane, butane, pentane and hexane. In some embodiments ofaspects provided herein, said cracking unit is sized to provide ahydrocarbon-containing stream having a residence time that is less than500 milliseconds. In some embodiments of aspects provided herein, thesystem further comprises a computer system that is programmed toregulate (i) a residence time of said hydrocarbon-containing stream insaid cracking unit and (ii) a temperature profile of said cracking unitto yield a product stream from said cracking unit with a C₂₊ alkene toC₂₊ alkane ratio that is greater than 1.

An aspect of the present disclosure provides a composition produced froman oxidative coupling of methane (OCM) process, the compositioncomprising ethylene and at least one of: (a) an acetone content that isgreater than zero and less than or equal to about 100 parts-per-million(ppm); (b) a carbon dioxide (CO₂) content that is greater than zero andless than or equal to about 100 ppm; (c) a carbon monoxide (CO) contentthat is greater than zero and less than or equal to about 100 ppm; (d)an acetylene content that is greater than zero and less than or equal toabout 2000 ppm; (e) a butene content that is greater than zero and lessthan or equal to about 200 ppm; and (f) relative to an ethyleneconcentration of said composition, a propylene content equal to orgreater than about 0.2%.

In some embodiments of aspects provided herein, said composition has anacetone content that is less than or equal to about 100 ppm, 50 ppm, 10ppm, 5 ppm, 1 ppm, 100 parts-per-billion (ppb), 50 ppb, 10 ppb, 5 ppb,or 1 ppb. In some embodiments of aspects provided herein, saidcomposition has a carbon dioxide (CO₂) content that is less than orequal to about 100 ppm, 50 ppm, 10 ppm, 5 ppm, 1 ppm, 100 ppb, 50 ppb,10 ppb, 5 ppb, or 1 ppb. In some embodiments of aspects provided herein,said composition has a carbon monoxide (CO) content that is less than orequal to about 100 ppm, 50 ppm, 10 ppm, 5 ppm, 1 ppm, 100 ppb, 50 ppb,10 ppb, 5 ppb, or 1 ppb. In some embodiments of aspects provided herein,said composition has an acetylene content that is less than or equal toabout 2000 ppm, 1000 ppm, 900 ppm, 800 ppm, 700 ppm, 600 ppm, 200 ppm,or 100 ppm. In some embodiments of aspects provided herein, saidcomposition has a butene content that is less than or equal to about 200ppm, 100 ppm, 50 ppm, or 10 ppm. In some embodiments of aspects providedherein, said composition has a propylene content that is greater than orequal to about 0.3%, 0.4%, 0.6%, 0.8%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%,or 9% relative to an ethylene content of said composition. In someembodiments of aspects provided herein, said composition has at leasttwo of (a)-(f). In some embodiments of aspects provided herein, saidcomposition has at least three of (a)-(f). In some embodiments ofaspects provided herein, said composition has at least four of (a)-(f).In some embodiments of aspects provided herein, said composition has atleast five of (a)-(f). In some embodiments of aspects provided herein,said composition has all of (a)-(f).

An aspect of the present disclosure provides a method, comprising: (a)providing a reactor comprising (i) an OCM section comprising an OCMcatalyst that facilitates the formation of OCM products from methane andan oxidizing agent, and (ii) a post-bed cracking section locateddownstream of said OCM catalyst section that facilitates cracking of OCMproducts, wherein said OCM section and said post-bed cracking sectionare integrated in said reactor; (b) directing said methane and saidoxidizing agent to said OCM section; (c) conducting OCM in said OCMsection to generate said OCM products; and (d) cracking at least aportion of said OCM products in said post-bed cracking section.

In some embodiments of aspects provided herein, the method furthercomprises (i) adding external ethane to said post-bed cracking sectionfrom a source other than said OCM products, and (ii) conducting crackingon said external ethane in said post-bed cracking section. In someembodiments of aspects provided herein, prior to said adding, saidexternal ethane is preheated to at least about 550° C. in the presenceof steam. In some embodiments of aspects provided herein, prior to saidadding, said external ethane is preheated to at least about 550° C. inthe presence of CO₂. In some embodiments of aspects provided herein, themethod further comprises: adding external propane to said post-bedcracking section from a source other than said OCM products; andconducting cracking on said external propane in said post-bed crackingsection. In some embodiments of aspects provided herein, prior to saidadding, said external propane is preheated to at least about 550° C. inthe presence of steam. In some embodiments of aspects provided herein,prior to said adding, said external propane is preheated to at leastabout 550° C. in the presence of CO₂. In some embodiments of aspectsprovided herein, the method further comprises: adding external ethanefrom a source other than said OCM products to said post-bed crackingsection at a first location; adding external propane from a source otherthan said OCM products to said post-bed cracking section at a secondlocation located downstream relative to said first location; andconducting cracking on said external ethane and said external propane insaid post-bed cracking section. In some embodiments of aspects providedherein, prior to said adding, said external ethane or said externalpropane is preheated to at least about 550° C. in the presence of steam.In some embodiments of aspects provided herein, prior to said adding,said external ethane or said external propane is preheated to at leastabout 550° C. in the presence of CO₂. In some embodiments of aspectsprovided herein, energy from said OCM products is used in said cracking.In some embodiments of aspects provided herein, said OCM productscomprise steam. In some embodiments of aspects provided herein, outlettemperature from said OCM catalyst section is greater than or equal toabout 700° C. In some embodiments of aspects provided herein, outlettemperature from said OCM catalyst section is greater than or equal toabout 700° C. and less than or equal to about 950° C. In someembodiments of aspects provided herein, residence time in said post-bedcracking section is less than or equal to about 200 milliseconds (ms).In some embodiments of aspects provided herein, residence time in saidpost-bed cracking section is less than or equal to about 100 ms. In someembodiments of aspects provided herein, residence time in said post-bedcracking section is less than or equal to about 50 ms. In someembodiments of aspects provided herein, said reactor comprises a fixedbed reactor. In some embodiments of aspects provided herein, saidreactor comprises a fluidized bed reactor. In some embodiments ofaspects provided herein, said reactor comprises a tubular reactor. Insome embodiments of aspects provided herein, said tubular reactorcomprises a molten salt heat exchange medium. In some embodiments ofaspects provided herein, said tubular reactor comprises a first reactorsection and a second reactor section downstream of said first reactorsection, said first reactor section being operated isothermally and saidsecond reactor section being operated adiabatically. In some embodimentsof aspects provided herein, said OCM catalyst section comprises asection of catalytically inert material. In some embodiments of aspectsprovided herein, said section of catalytically inert material comprisescatalytically inert particles that are different in size from OCMcatalyst particles in said OCM catalyst section. In some embodiments ofaspects provided herein, residence time in said post-bed crackingsection is at least about 10 times shorter than residence time in saidOCM catalyst section.

An aspect of the present disclosure provides an oxidative coupling ofmethane (OCM) system, comprising: (a) a feed stream comprising methane;(b) a first OCM reactor supplied by said feed stream, wherein said firstOCM reactor comprises an OCM catalyst that reacts a portion of saidmethane in said feed stream with an oxidizing agent to generate a firstOCM product stream; and (c) a second OCM reactor downstream of saidfirst OCM reactor which receives said first OCM product stream from saidfirst OCM reactor, wherein said second OCM reactor is supplied by saidfeed stream via a bypass of said first OCM reactor and said second OCMreactor comprises an OCM catalyst that generates a second OCM productstream from at least a portion of said methane in said feed stream.

In some embodiments of aspects provided herein, the system furthercomprises a mixing zone downstream of said first OCM reactor, whereinsaid mixing zone (i) receives said first OCM product stream from saidfirst OCM reactor and said portion of said methane from said feedstream, and (ii) mixes at least a portion of said first OCM productstream with said portion of said methane from said feed stream.

An aspect of the present disclosure provides a method of chemicallooping for an oxidative coupling of methane (OCM) system, comprising:(a) oxidizing a reduced oxygen carrier in a first catalyst bed, therebyproducing an oxidized oxygen carrier; (b) transferring said oxidizedoxygen carrier to a second catalyst bed; and (c) conducting OCM in saidsecond catalyst bed, wherein said oxidized oxygen carrier providesoxygen for said OCM, thereby producing an OCM product.

In some embodiments of aspects provided herein, said second catalyst bedis substantially free of molecular oxygen. In some embodiments ofaspects provided herein, said second catalyst bed is free of molecularoxygen. In some embodiments of aspects provided herein, said secondcatalyst bed is substantially free of N₂. In some embodiments of aspectsprovided herein, said second catalyst bed is free of N₂. In someembodiments of aspects provided herein, said OCM product issubstantially free of N₂. In some embodiments of aspects providedherein, said OCM product is free of N₂. In some embodiments of aspectsprovided herein, said reduced oxygen carrier or said oxidized oxygencarrier comprises material selected from the group consisting of: Ni₂O₃,Al₂O₃, CeO₂, MnO₂, SiO₂, perovskite, La-based material, mixed oxide, orcombinations thereof.

An aspect of the present disclosure provides a method for the oxidativecoupling of methane (OCM) in a reactor to generate hydrocarbon compoundscontaining at least two carbon atoms (C₂₊ compounds), comprising: (a)mixing a first gas stream comprising methane with a second gas streamcomprising oxygen to form a third gas stream comprising methane andoxygen; (b) performing an OCM reaction in a first section of saidreactor using said third gas stream to produce a first product streamcomprising one or more C₂₊ compounds; and (c) performing an OCM reactionin a second section of said reactor using a fourth gas stream comprisingmethane in the presence of an oxygen regenerated catalyst to produce asecond product stream comprising one or more C₂₊ compounds.

In some embodiments of aspects provided herein, said first sectionincludes an OCM catalyst and said second section includes an oxygen-richOCM catalyst. In some embodiments of aspects provided herein, saidsecond section does not include an external oxygen source directlycoupled to said second section. In some embodiments of aspects providedherein, a source of oxygen for OCM in said second section is from saidoxygen regenerated catalyst.

An aspect of the present disclosure provides a reactor system forperforming oxidative coupling of methane (OCM) to generate hydrocarboncompounds containing at least two carbon atoms (C₂₊ compounds),comprising a catalyst that performs an OCM reaction to produce a productstream comprising one or more C₂₊ compounds, wherein said catalyst issupported on beta-SiC.

An aspect of the present disclosure provides a reactor system forperforming oxidative coupling of methane (OCM) to generate hydrocarboncompounds containing at least two carbon atoms (C₂₊ compounds),comprising a catalyst bed having an OCM catalyst that performs an OCMreaction to produce a product stream comprising one or more C₂₊compounds, wherein the concentration of said OCM catalyst varies by atleast 5% across said catalyst bed.

In some embodiments of aspects provided herein, said concentration ofsaid OCM catalyst varies by at least 10% across said catalyst bed. Insome embodiments of aspects provided herein, said concentration of saidOCM catalyst varies by at least 20% across said catalyst bed. In someembodiments of aspects provided herein, said concentration of said OCMcatalyst varies by at least 50% across said catalyst bed.

An aspect of the present disclosure provides a reactor system forperforming oxidative coupling of methane (OCM) to generate hydrocarboncompounds containing at least two carbon atoms (C₂₊ compounds),comprising a tubular reactor including an OCM catalyst bed that containsan OCM catalyst that performs an OCM reaction to produce a productstream comprising one or more C₂₊ compounds, wherein said catalyst bedhas a composition gradient that decreases radially from a center to aperimeter of said bed.

An aspect of the present disclosure provides a method for the oxidativecoupling of methane (OCM) in a reactor having an OCM catalyst bed togenerate hydrocarbon compounds containing at least two carbon atoms (C₂₊compounds), comprising: (a) mixing a first gas stream comprising methanewith a second gas stream comprising oxygen to form a third gas streamcomprising methane and oxygen, wherein the linear velocity of said thirdgas stream through said OCM catalyst bed is less than or equal to about0.5 meters per second (m/s); and (b) performing an oxidative coupling ofmethane (OCM) reaction using said third gas stream to produce a productstream comprising one or more C₂₊ compounds.

In some embodiments of aspects provided herein, the linear velocity ofsaid third gas stream through said OCM catalyst bed is less than orequal to about 0.3 meters per second (m/s). In some embodiments ofaspects provided herein, the linear velocity of said third gas streamthrough said OCM catalyst bed is less than or equal to about 0.1 metersper second (m/s).

An aspect of the present disclosure provides a method for the oxidativecoupling of methane (OCM) in a reactor to generate hydrocarbon compoundscontaining at least two carbon atoms (C₂₊ compounds), comprising: (a)mixing a first gas stream comprising methane with a second gas streamcomprising oxygen to form a third gas stream comprising methane andoxygen; (b) performing an OCM reaction in said reactor using said thirdgas stream to produce a product stream comprising one or more C₂₊compounds; and (c) alternately and sequentially switching an injectionlocation of said third stream into said reactor between a firstinjection location and a second injection location.

An aspect of the present disclosure provides a reactor system forperforming oxidative coupling of methane (OCM) in reactor to generatehydrocarbon compounds containing at least two carbon atoms (C₂₊compounds), comprising: (a) an OCM catalyst bed containing an OCMcatalyst that performs an OCM reaction using methane and oxygen toproduce a product stream comprising one or more C₂₊ compounds; (b) aninlet manifold in said OCM catalyst bed that includes a plurality oftubes, wherein said inlet manifold directs a gas stream comprising saidmethane and oxygen into said OCM catalyst bed; and (c) an outletmanifold in said OCM catalyst bed that includes a plurality of tubes,wherein said outlet manifold directs said product stream from said OCMcatalyst bed, wherein said inlet manifold and said outlet manifold arepositioned in an interdigitated sandwich configuration.

An aspect of the present disclosure provides a reactor system forperforming oxidative coupling of methane (OCM) to generate hydrocarboncompounds containing at least two carbon atoms (C₂₊ compounds),comprising: (a) an OCM reactor having a reactor inlet, a catalyst bedand a reactor outlet, wherein said reactor inlet directs methane andoxygen to said catalyst bed to perform an OCM reaction in the presenceof an OCM catalyst to yield a product stream comprising one or more C₂₊compounds, which product stream is directed out of said catalyst bed viasaid reactor outlet; and (b) a heat exchanger located in said reactorupstream of said reactor outlet, wherein said heat exchanger is inthermal communication with said product stream.

In some embodiments of aspects provided herein, said heat exchanger isin thermal communication with said catalyst bed and/or said reactoroutlet.

An aspect of the present disclosure provides a method for the oxidativecoupling of methane to generate hydrocarbon compounds containing atleast two carbon atoms (C₂₊ compounds) in a reactor, comprising: (a)mixing a first gas stream comprising methane with a second gas streamcomprising oxygen to form a third gas stream comprising methane andoxygen; (b) performing an oxidative coupling of methane (OCM) reactionusing said third gas stream and an OCM catalyst bed to produce a productstream comprising one or more C₂₊ compounds; and (c) injecting a fourthstream comprising hydrocarbons into a catalytically inert region of saidOCM catalyst bed.

An aspect of the present disclosure provides a method, comprising: (a)providing a reactor comprising (i) an OCM section comprising an OCMcatalyst that facilitates the formation of OCM products from methane andan oxidizing agent, and (ii) a post-bed cracking section locateddownstream of said OCM catalyst section that facilitates cracking of atleast a portion of said OCM products, wherein said OCM section and saidpost-bed cracking section are integrated in said reactor; (b) directingsaid methane and said oxidizing agent to said OCM section; (c)conducting OCM in said OCM section to generate said OCM products; (d)mixing said OCM products with a CO₂ stream to produce a cracking stream;and (e) cracking at least a portion of said OCM products in saidcracking stream in said post-bed cracking section.

An aspect of the present disclosure provides a method, comprising: (a)providing a reactor comprising (i) an OCM section comprising an OCMcatalyst that facilitates the formation of OCM products from methane andan oxidizing agent, said OCM section comprising an isothermal subsectionand an adiabatic subsection, and (ii) a post-bed cracking sectionlocated downstream of said OCM catalyst section that facilitatescracking of at least a portion of said OCM products, wherein said OCMsection and said post-bed cracking section are integrated in saidreactor; (b) directing said methane and said oxidizing agent to said OCMsection; (c) conducting OCM in said OCM section to generate said OCMproducts; and (d) cracking at least a portion of said OCM products insaid post-bed cracking section.

Additional aspects and advantages of the present disclosure will becomereadily apparent to those skilled in this art from the followingdetailed description, wherein only illustrative embodiments of thepresent disclosure are shown and described. As will be realized, thepresent disclosure is capable of other and different embodiments, andits several details are capable of modifications in various obviousrespects, all without departing from the disclosure. Accordingly, thedrawings and description are to be regarded as illustrative in nature,and not as restrictive.

INCORPORATION BY REFERENCE

All publications, patents, and patent applications mentioned in thisspecification are herein incorporated by reference to the same extent asif each individual publication, patent, or patent application wasspecifically and individually indicated to be incorporated by reference.

BRIEF DESCRIPTION OF THE FIGURES

The novel features of the invention are set forth with particularity inthe appended claims. A better understanding of the features andadvantages of the present invention will be obtained by reference to thefollowing detailed description that sets forth illustrative embodiments,in which the principles of the invention are utilized, and theaccompanying drawings or figures (also “FIG.” and “FIGS.” herein), ofwhich:

FIG. 1 schematically illustrates a system for the oxidative coupling ofmethane (OCM);

FIG. 2A shows an OCM system comprising methane and oxygen containing gasstreams;

FIG. 2B shows the OCM system of FIG. 2A with a catalyst adjacent to amixer;

FIG. 3A shows an OCM system comprising a methane and oxygen containinggas stream, a distributor and catalyst bed; FIG. 3B shows the OCM systemof FIG. 3A with the distributor situated in an inert packing medium;FIG. 3C shows the OCM system in which the distributor is situated in thecatalyst bed;

FIGS. 4A and 4B are schematic side and cross-sectional side views,respectively, of an OCM reactor designed with an airfoil-shaped mixer;

FIG. 5 schematically illustrates a blade that may be employed for use asa rib of a mixer;

FIG. 6 is a plot from a computational fluid dynamics (CFD) analysis ofan airfoil-shaped mixer in fluid communication with an OCM reactor;

FIG. 7A shows an OCM system with a fluid flow conduit that is directedthrough an OCM catalyst bed and in fluid communication with a gasdistributor; FIG. 7B shows the OCM system of FIG. 7A with the gasdistributor situated in the catalyst bed;

FIG. 8 shows an OCM system in which OCM reaction heat is used to heatinlet air;

FIG. 9 is a graph of temperature (y-axis) as a function of heatexchanger efficiency (x-axis) for various elements the OCM system ofFIG. 8;

FIGS. 10A, 10B and 10C are isometric, side and cross-sectional sideviews, respectively, of an OCM system that is an integrated heatexchanger and gas injection system;

FIG. 11A shows an OCM reactor that is integrated with a heat exchanger;FIGS. 11B and 11C are schematic cross-sectional and side views,respectively, of an integrated OCM reactor and heating element;

FIG. 12 shows a schematic of an OCM reactor with inlet and outletmanifolds;

FIG. 13 schematically illustrates a system for the oxidative coupling ofmethane (OCM);

FIG. 14 shows a system comprising an OCM reactor with a catalyst unitand a cracking unit downstream of the catalyst unit;

FIG. 15A shows an OCM reactor comprising an integrated catalyst unit andcracking unit;

FIG. 15B shows an OCM reactor comprising a radial fixed bed catalystunit;

FIG. 16 shows a plot of a thermodynamic and kinetic modeling studyshowing the mole fraction of ethylene as a function of the mole fractionof ethane at various residence times (50 ms, 100 ms and 200 ms);

FIG. 17 shows a plot of a thermodynamic and kinetic modeling studyshowing ethane conversion and C₂ ratio as a function of mole fraction ofethane at various residence times (50 ms, 100 ms and 200 ms);

FIGS. 18A-18D show schematically illustrated various OCM reactors withalkane injections lines for introducing alkanes to the OCM reactors;

FIG. 19 shows a schematic of an OCM reactor with an inert packing zone;

FIG. 20 shows a computer system that is programmed or otherwiseconfigured to regulate OCM reactions;

FIG. 21 shows a plot of data for ethane conversion and ethyleneselectivity in a post-bed cracking (PBC) process;

FIG. 22 shows an example of performing an OCM reaction with bypass;

FIG. 23 shows an example of a reactor for performing an OCM reactionwith bypass;

FIG. 24 shows an example of performing an OCM reaction with multiplefeedstocks;

FIG. 25 shows an example of a reactor for performing an OCM reactionwith multiple feedstocks;

FIG. 26 shows an example of the effect of selectivity as a function ofpeak bed temperature for OCM with bypass;

FIG. 27 shows an example of the effect of selectivity as a function ofinlet temperature for OCM with bypass;

FIG. 28 shows an example of a reactor with heat transfer capabilityusing molten salts;

FIG. 29A-D show examples of catalyst packing geometries;

FIG. 30 shows an example of the effect of catalyst packing geometry;

FIG. 31 shows an example of a low linear velocity OCM reactor;

FIG. 32 shows an example of the effect of performing the OCM reaction atlow linear velocity;

FIG. 33 shows an example of a reactor system for performing OCM withflow reversal;

FIG. 34 shows an example of an expected temperature profile whenperforming the OCM reaction with flow reversal;

FIG. 35 shows an example of a mixer for injecting alkanes into an OCMreactor; and

FIG. 36 shows an example of a simulation of gas flow through a mixer.

DETAILED DESCRIPTION

While various embodiments of the invention have been shown and describedherein, it will be obvious to those skilled in the art that suchembodiments are provided by way of example only. Numerous variations,changes, and substitutions may occur to those skilled in the art withoutdeparting from the invention. It should be understood that variousalternatives to the embodiments of the invention described herein may beemployed.

The term “OCM process,” as used herein, generally refers to a processthat employs or substantially employs an oxidative coupling of methane(OCM) reaction. An OCM reaction can include the oxidation of methane toa hydrocarbon and water, and involves an exothermic reaction. In an OCMreaction, methane can be partially oxidized to one or more C₂₊compounds, such as ethylene. In an example, an OCM reaction is2CH₄+O₂→C₂H₄+2H₂O. An OCM reaction can yield C₂₊ compounds. An OCMreaction can be facilitated by a catalyst, such as a heterogeneouscatalyst. Additional by-products of OCM reactions can include CO, CO₂,H₂, as well as hydrocarbons, such as, for example, ethane, propane,propene, butane, butane, and the like.

The term “non-OCM process,” as used herein, generally refers to aprocess that does not employ or substantially employ an oxidativecoupling of methane reaction. Examples of processes that may be non-OCMprocesses include non-OCM hydrocarbon processes, such as, for example,non-OCM processes employed in hydrocarbon processing in oil refineries,a natural gas liquids separations processes, steam cracking of ethane,Fischer-Tropsch processes, and the like.

The terms “C₂₊” and “C₂₊ compound,” as used herein, generally refer to acompound comprising two or more carbon atoms, e.g., C₂, C₃ etc. C₂₊compounds include, without limitation, alkanes, alkene, alkynes,aldehydes, ketones, aromatics esters and carboxylic acids containing twoor more carbon atoms. Examples of C₂₊ compounds include ethane, ethene,ethyne, propane, propene and propyne, etc.

The term “non-C₂₊ impurities,” as used herein, generally refers tomaterial that does not include C₂₊ compounds. Examples of non-C₂₊impurities, which may be found in certain OCM reaction product streams,include nitrogen (N₂), oxygen (O₂), water (H₂O), argon (Ar), hydrogen(H₂) carbon monoxide (CO), carbon dioxide (CO₂) and methane (CH₄).

The term “methane conversion,” as used herein, generally refers to thepercentage or fraction of methane introduced into the reaction that isconverted to a product other than methane.

The term “C₂₊ selectivity,” as used herein, generally refers to thepercentage of all carbon containing products of an oxidative coupling ofmethane (“OCM”) reaction that are the desired or otherwise preferableC₂₊ products, e.g., ethane, ethylene, propane, propylene, etc. Althoughprimarily stated as C₂₊ selectivity, it will be appreciated thatselectivity may be stated in terms of any of the desired products, e.g.,just C₂, or just C₂ and C₃.

The term “C₂₊ yield,” as used herein, generally refers to the amount ofcarbon that is incorporated into a C₂₊ product as a percentage of theamount of carbon introduced into a reactor in the form of methane. Thismay generally be calculated as the product of the conversion and theselectivity divided by the number of carbon atoms in the desiredproduct. C₂₊ yield is typically additive of the yield of the differentC₂₊ components included in the C₂₊ components identified, e.g., ethaneyield+ethylene yield+propane yield+propylene yield etc.).

The term “airfoil” (or “aerofoil” or “airfoil section”), as used herein,generally refers to the cross-sectional shape of a blade. A blade mayhave one or more airfoils. In an example, a blade has a cross-sectionthat is constant along a span of the blade, and the blade has oneairfoil. In another example, a blade has a cross-section that variesalong a span of the blade, and the blade has a plurality of airfoils.

The term “auto-ignition” or “autoignition,” as used herein in thecontext of temperature, generally refers to the lowest temperature atwhich a substance, given sufficient time, will spontaneously ignitewithout an external source of ignition, such as a flame or spark. Use ofthe term “auto-ignites” with reference to oxygen refers to the amount ofoxygen that reacts with (e.g., combustion reaction) any or allhydrocarbons that are mixed with oxygen (e.g., methane).

The term “substantially equivalent,” as used herein in the context ofmethane concentration, generally means that the methane concentration iswithin approximately plus or minus 80%, 70%, 60%, 50%, 40%, or 30%, andpreferably within plus or minus 20%, 10%, or even 5% of the methaneconcentration typically passed into an existing fractionation train of agas facility or cracker facility.

OCM Processes

In some OCM processes, methane reacts with oxygen over a suitablecatalyst to generate ethylene, e.g., 2CH₄+O₂→C₂H₄+2H₂O (See, e.g.,Zhang, Q., Journal of Natural Gas Chem., 12:81, 2003; Olah, G.“Hydrocarbon Chemistry”, Ed. 2, John Wiley & Sons (2003)). This reactionis exothermic (ΔH=−67 kcals/mole) and has typically been shown to occurat very high temperatures (>700° C.). Although the detailed reactionmechanism is not fully characterized, experimental evidence suggeststhat free radical chemistry is involved. (Lunsford, J. Chem. Soc., Chem.Comm., 1991; H. Lunsford, Angew. Chem., Int. Ed. Engl., 34:970, 1995).In the reaction, methane (CH₄) is activated on the catalyst surface,forming methyl radicals which then couple in the gas phase to formethane (C₂H₆), followed by dehydrogenation to ethylene (C₂H₄). Severalcatalysts have shown activity for OCM, including various forms of ironoxide, V₂O₅, MoO₃, Co₃O₄, Pt—Rh, Li/ZrO₂, Ag—Au, Au/Co₃O₄, Co/Mn, CeO₂,MgO, La₂O₃, Mn₃O₄, Na₂WO₄, MnO, ZnO, and combinations thereof, onvarious supports. A number of doping elements have also proven to beuseful in combination with the above catalysts.

Since the OCM reaction was first reported over thirty years ago, it hasbeen the target of intense scientific and commercial interest, but thefundamental limitations of the conventional approach to C—H bondactivation appear to limit the yield of this attractive reaction underpractical operating conditions. Specifically, numerous publications fromindustrial and academic labs have consistently demonstratedcharacteristic performance of high selectivity at low conversion ofmethane, or low selectivity at high conversion (J. A. Labinger, Cat.Lett., 1:371, 1988). Limited by this conversion/selectivity threshold,no OCM catalyst has been able to exceed 20-25% combined C₂ yield (i.e.ethane and ethylene), and more importantly, all such reported yieldsoperate at extremely high temperatures (>800 C) and/or low pressures (<1barg). Catalysts and processes have been described for use in performingOCM in the production of ethylene from methane at substantially morepracticable temperatures, pressures and catalyst activities. These aredescribed in commonly owned Published U.S. Patent Application Nos.2012/0041246, 2013/0023079, 2013/165728, and U.S. patent applicationSer. Nos. 13/936,783 and 13/936,870 (both filed Jul. 8, 2013), the fulldisclosures of each of these is incorporated herein by reference in itsentirety for all purposes.

A wide set of competitive reactions can occur simultaneously orsubstantially simultaneously with the OCM reaction, including totalcombustion of both methane and all partial oxidation products. An OCMprocess can provide C₂₊ compounds as well as non-C₂₊ impurities. Naturalgas can be used to provide methane, in some cases combined with arecycle stream from downstream separation units. Air, enriched air, orpure oxygen can be used to supply the oxygen required for the OCMreaction. Oxygen can be extracted from air, for example, in a cryogenicair separation unit.

To carry out an OCM reaction in conjunction with preferred catalyticsystems, the methane and oxygen containing gases generally need to bebrought up to appropriate reaction temperatures, e.g., typically inexcess of 450° C. for preferred catalytic OCM processes, before beingintroduced to the catalyst, in order to allow initiation of the OCMreaction. Once that reaction begins or “lights off”, then the heat ofthe reaction is typically sufficient to maintain the reactor temperatureat appropriate levels. Additionally, these processes may operate at apressure above atmospheric pressure, such as in the range of about 1 to30 bars (absolute).

Providing OCM reactants at the above-described elevated temperatures andpressures presents a number of challenges and process costs. Forexample, as will be appreciated, heating a mixed gas of methane andoxygen can present numerous challenges. In particular, mixtures ofmethane and oxygen, at temperatures in excess of about 450° C. and apressure above atmospheric, can be in the auto-ignition zone, i.e.,given sufficient time, the mixture can spontaneously combust without theneed of any ignition source. Additionally, the provision of thermalenergy to heat the reactants prior to entering a catalytic reactor canhave substantial costs in terms of energy input to the process.

At least some component of the auto-ignition risk is alleviated bypre-heating the methane containing gas and oxygen containing gascomponents to reaction temperature separately. While this avoidsautoignition in the heated separate gas streams, in some cases, the OCMprocess necessarily requires the mixing of these two gas streams priorto carrying out the OCM reaction, at which point, the auto-ignition riskresurfaces. Minimizing the residence time of these mixed, heated gasesprior to contact with the catalyst bed within the reactor is desired inorder to reduce or eliminate the possibility of auto-ignition of thereactant gases, and the consequent negative implications of combustion.Accordingly, in at least one aspect, the present invention providesimproved gas mixing devices systems and methods for complete, rapid andefficient mixing of gas streams so that the mixed streams can be morerapidly introduced to the catalyst bed.

The present disclosure provides processes, devices, methods and systemsthat address these challenges and costs by allowing for thepre-conditioning of reactant gases prior to their introduction into acatalytic reactor or reactor bed, in a safe and efficient manner. Suchpre-conditioning can include (i) mixing of reactant streams, such as amethane-containing stream and a stream of an oxidizing agent (e.g.,oxygen) in or prior an OCM reactor or prior to directing the streams tothe OCM reactor, (ii) heating or pre-heating the methane-containingstream and/or the stream of the oxidizing agent using, for example, heatfrom the OCM reactor, or (iii) a combination of mixing and pre-heating.

Mixing Devices, Systems and Methods

In an aspect of the present disclosure, pre-conditioning of OCM reactantstreams is achieved by mixing using mixer devices, systems and methodsfor OCM processes. Such devices or systems can overcome the limitationsabove by i) mixing the methane-containing and oxygen-containing streamswith the required degrees of uniformity in terms of temperature,composition and velocity; and ii) mixing the methane-containing andoxygen-containing streams substantially completely, rapidly andefficiently in order to minimize the residence time of the heated mixedgases before they can be contacted with and reacted in the catalyst bed,which will preferably be less than, and more preferably, substantiallyless than the amount of time for autoignition of the mixed heated gasesto occur.

Required composition uniformity can be such that the deviation of themost oxygen-rich and oxygen-poor post-mixing areas in terms of CH₄/O₂ratio is less than 50%, 40%, 30%, 20%, 15%, 10%, 5%, 4%, 3%, 2%, or 1%compared to a perfectly mixed stream. Required temperature uniformitycan be such that the deviation of the hottest and coldest post-mixingzones from the temperature of the ideally mixed stream is less thanabout 30° C., 20° C., 10° C., or 5° C. Required velocity uniformity canbe such that the deviation in flow of the post-mixing areas with thelargest and smallest flow from the flow of the ideally mixed stream isless than 50%, 40%, 30%, 20%, 15%, 10%, 5%, 4%, 3%, 2%, or 1%. Anylarger deviations of these variables from the average may cause thecatalytic bed located downstream of the mixer to perform with a reducedefficiency. Mixers of the present disclosure can aid in achieving adesired degree of compositional, pressure, temperature and/or flowuniformity in a time period lower than the auto-ignition delay time,such as within a time period from about 5 milliseconds (ms) to 200 msand/or a range of flow rates from about 1 Million standard cubic feetper day (MMSCFD) to 2,000 MMSCFD. In some embodiments, the auto-ignitiondelay time is from about 10 milliseconds (ms) to 1000 ms, or 20 ms to500 ms, at a pressure from about 1 bar (absolute) and 100 bars, or 1 barto 30 bars, and a temperature from about 300° C. to 900° C., or 400° C.and 750° C.

If any portion of the mixed stream is allowed to spend longer than theauto-ignition delay time in the mixing zone before coming in contactwith a catalyst in the OCM reactor, this particular portion canauto-ignite and propagate combustion throughout the entire stream. Insome cases, 100% of the stream spends less than the auto-ignition time,which may require the mixer to be characterized by a substantiallynarrow distribution of residence times and the absence of a right tailin the distribution curve beyond the auto-ignition threshold. Such amixer can provide a non-symmetric distribution of residence times.

An aspect of the present disclosure provides an oxidative coupling ofmethane process comprising a mixing member or device (or mixer) in fluidcommunication with an OCM reactor. The mixer is configured to mix astream comprising methane and a stream comprising oxygen to yield astream comprising methane and oxygen, which is subsequently directed tothe OCM reactor to yield products comprising hydrocarbon compounds. Thehydrocarbon compounds can subsequently undergo separation into variousstreams, some of which can be recycled to the mixer and/or the OCMreactor.

The hydrocarbon compounds can include compounds with two or more carbonatoms (also “C₂₊ compounds” herein). The hydrocarbon compounds caninclude C₂₊ compounds at a concentration (e.g., mole % or volume %) ofat least about 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, or99%. In some situations, the hydrocarbon compounds substantially orexclusively include C₂₊ compounds, such as, for example, C₂₊ compoundsat a concentration of least about 60%, 70%, 80%, 90%, 95%, 99%, or99.9%.

Mixing can be employed in a mixer fluidically coupled to an OCM reactor.The mixer can be integrated with the OCM reactor, or be a standaloneunit. In some examples, the mixer is upstream of the OCM reactor. Inother examples, the mixer is at least partly or substantially integratedwith the OCM reactor. For example, the mixer can be at least partly orsubstantially immersed in a reactor bed of the OCM reactor. The reactorbed can be a fluidized bed.

Systems and methods of the present disclosure can maximize theefficiency of an OCM reaction and reduce, if not eliminate, undesiredreactions.

Fluid properties can be selected such that methane and an oxidizingagent (e.g., O₂) do not auto-ignite at a location that is before thecatalyst of the OCM reactor. For instance, a stream comprising methaneand oxygen can have a composition that is selected such that at most 5%,4%, 3%, 2%, 1%, 0.1%, or 0.01% of the oxygen in the mixed gas streamauto-ignites. The fluid properties include the period of time in whichmethane is in contact with oxygen (or another oxidizing agent). Theresidence time can be minimized so as to preclude auto-ignition. In somecases, the stream comprising methane and oxygen can have a substantiallynon-symmetric distribution of residence (or delay) times along adirection of flow of said third stream. The residence (or delay) time isthe period in which a stream comprising methane and oxygen does notauto-ignite. In some examples, the distribution of residence times isskewed towards shorter residence times, such as from about 5 ms to 50ms. Auto-ignition delay time may be primarily a function of temperatureand pressure and, secondarily, of composition. In some cases, the higherthe pressure or the temperature, the shorter the auto-ignition delaytime. Similarly, the closer the composition to the stoichiometryrequired for combustion, the shorter the auto-ignition delay time.Diagrams based on empirical data and thermodynamic correlations may beused to determine i) the auto-ignition region (i.e., the thresholdvalues of temperature, pressure and composition above or below whichauto-ignition may occur); and ii) the auto-ignition delay time insidethe auto-ignition region. Once the auto-ignition delay time isdetermined for the desired or otherwise predetermined operatingconditions, the mixer may be designed such that 100% of the mixed streamspends less than the auto-ignition time in the mixer itself prior tocontacting the OCM catalyst.

During mixing, flow separation may cause a portion of the flow to spenda substantially long period of time in a limited region due to eitherthe gas continuously recirculating in that region or being stagnant. Inat least some cases, flow separation causes this portion of the flow tospend more time than the auto-ignition time prior to contact with thecatalyst, thus leading to auto-ignition and propagation of thecombustion to the adjacent regions, and eventually, to the entirestream.

Mixers of the present disclosure may be operated in a manner thatdrastically reduces, if not eliminates, flow separation. In somesituations, fluid properties (e.g., flow regimes) and/or mixergeometries are selected such that upon mixing a stream comprisingmethane with a stream comprising oxygen in a mixer flow separation doesnot occur between the mixer and the first gas stream, the second gasstream, and/or the third gas stream.

FIG. 1 shows an OCM system 100 comprising a mixer 101, an OCM reactor102 downstream of the mixer 101, and a separation unit 103 downstream ofthe OCM reactor 102. The arrows indicate the direction of fluid flow. Afirst fluid stream (“stream”) 104 comprising methane (CH₄) and a secondfluid stream 105 comprising oxygen (O₂) are directed into the mixer 101,where they are mixed to form a third mixed gas stream 106 that isdirected into the OCM reactor 102. The second fluid stream 105 maycomprise CH₄ (e.g., natural gas) and O₂ mixed and maintained at atemperature below the auto-ignition temperature. In some cases, dilutingpure O₂ with methane may be desirable to enable relatively simplermaterial of construction for the mixer compared to situations in whichpure O₂ is used. In situations where pure O₂ is used, materials such asHastelloy X, Hastelloy G, Nimonic 90, and others can be used as they arehigh temperature stable and resist metal ignition in oxygenenvironments. Other materials can be used in the case of oxygen dilutedwith methane. In the OCM reactor 102, methane and oxygen react in thepresence of a catalyst provided within reactor 102, to form C₂₊compounds, which are included in a fourth stream 107. The fourth stream107 can include other species, such as non-C₂₊ impurities like Ar, H₂,CO, CO₂, H₂O, N₂, NO₂ and CH₄. The fourth stream 107 is then optionallydirected to other unit operations for processing the outlet gas stream107, such as separation unit 103, used for separation of at least some,all, or substantially all of the C₂₊ compounds from other components inthe fourth stream 107 to yield a fifth stream 108 and a sixth stream109. The fifth stream 108 can include C₂₊ compounds at a concentration(e.g., mole % or volume %) that is at least 10%, 20%, 30%, 40%, 50%,60%, 70%, 80%, 90%, 95%, or 99%, and the sixth stream 109 can includeC₂₊ compounds at a concentration that is less than about 99%, 95%, 90%,80%, 70%, 60%, 50%, 40%, 30%, 20%, or 10%. The concentration of C₂₊compounds in the fifth stream 108 can be higher than the concentrationof C₂₊ compounds in the sixth stream 109. The sixth stream 109 caninclude other species, such as Ar, H₂, CO, CO₂, H₂O, N₂, NO₂ and CH₄. Atleast some, all or substantially all of CH₄ and/or O₂ in the sixthstream 109 may optionally be recycled to the mixer 101 and/or the OCMreactor 102 in a seventh stream 110. Although illustrated in FIG. 1 as aseparate unit operation, the mixer component of the system may beintegrated into one or more unit operations of an overall OCM processsystem. For example, in preferred aspects, mixer 101 is an integratedportion of reactor 102, positioned immediately adjacent to the catalystbed within the reactor 102, so that that the mixed gas stream 106 may bemore rapidly introduced to the reactor's catalyst bed, in order tominimize the residence time of mixed stream 106.

Methane in the first fluid stream 104 can be provided from any of avariety of methane sources, including, e.g., a natural gas source (e.g.,natural gas reservoir) or other petrochemical source, or in some casesrecycled from product streams. Methane in the first fluid stream may beprovided from an upstream non-OCM process.

The product stream 108 can be directed to one or more storage units,such as C₂₊ storage. In some cases, the product stream can be directedto a non-OCM process.

Fluid properties (e.g., flow regimes) may be selected such that optimummixing is achieved. Fluid properties can be selected from one or more offlow rate, temperature, pressure, and concentration. Fluid propertiescan be selected to achieve a given (i) temperature variation in thethird stream 106, (ii) variation of concentration of methane to theconcentration of oxygen in the third stream 106, and/or (iii) variationof the flow rate of the third stream 106. Any one, two or all three of(i)-(iii) can be selected. In some cases, the temperature variation ofthe third stream 106 is less than about 100° C., 50° C., 40° C., 30° C.,20° C., 10° C., 5° C., or 1° C. The variation of the concentration ofmethane to the concentration of oxygen (CH₄/O₂) in the third stream 106can be less than about 50%, 40%, 30%, 20%, 15%, 10%, 5%, 4%, 3%, 2%, or1% compared to a perfectly mixed (or ideal) stream. The variation of theflow rate of the third stream 106 can be less than about 50%, 40%, 30%,20%, 15%, 10%, 5%, 4%, 3%, 2%, or 1%. Such variations can be as comparedto a perfectly mixed or thermally equilibrated stream and may be takenalong a direction that is orthogonal to the direction of flow.Variations can be measured at the exit plane of 106, for example.

The mixer 101 can mix the first stream 104 and the second stream 105 togenerate a stream characterized by uniform or substantially uniformcomposition, temperature, pressure and velocity profiles across a crosssection of a mixing zone of the mixer 101 or reactor 102 (e.g., along adirection that is orthogonal to the direction of flow). Uniformity canbe described in terms of deviation of the extremes from an averageprofile. For example, if the various streams possess differenttemperatures, the resulting profile of the mixed stream can show amaximum deviation of +/−1 to 20° C. between the hottest and coldestareas compared to the ideal (e.g., perfectly mixed) stream. Similarly,if the various streams possess different compositions, the resultingprofile of the mixed stream may show a maximum deviation of +/−0.1 to 20mole % of all reacting compounds compared to the composition of theideal stream. Similar metrics can be used for velocity and pressureprofiles.

In some cases, the system 100 can include at least 1, 2, 3, 4, 5, 6, 7,8, 9, or 10 separation units. In the illustrated example, the system 100includes one separation unit 103. The separation unit 103 can be, forexample, a distillation column, scrubber, or absorber. If the system 100includes multiple separation units 103, the separation units 103 can bein series and/or in parallel.

The system 100 can include any number of mixers and OCM reactors. Thesystem 100 can include at least 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 mixers101. The system 100 can include at least 1, 2, 3, 4, 5, 6, 7, 8, 9, or10 reactors 102. The mixers 101 can be in series and/or in parallel. Thereactors 102 can be in series and/or in parallel.

Although described for illustration of preferred aspects as gas streamspassing into, through and out of the reactor systems in FIG. 1, it willbe appreciated that the streams 104, 105, 106, 107, 108, 109 and 110 canbe gaseous streams, liquid streams, or a combination of gaseous andliquid streams. In some examples, the streams 104 and 105 are gaseousstreams, and the stream 108 and 109 are liquid streams. In someexamples, the streams 104, 105, and 109 are gaseous streams, and thestream 108 is a liquid stream.

In some cases, the system 100 includes multiple OCM reactors 102. TheOCM reactors 102 can be the same, similar or dissimilar reactors orreactor types arranged in series or parallel processing trains.

The OCM reactor 102 can include any vessel, device, system or structurecapable of converting at least a portion of the third stream 106 intoone or more C₂₊ compounds using an OCM process. The OCM reactor 102 caninclude a fixed bed reactor where the combined methane/oxygen gasmixture is passed through a structured bed, a fluidized bed reactorwhere the combined methane/oxygen mixture is used to fluidize a solidcatalyst bed, and/or a membrane type reactor where the combinedmethane/oxygen mixture passes through an inorganic catalytic membrane.

The OCM reactor 102 can include a catalyst that facilitates an OCMprocess. The catalyst may include a compound including at least one ofan alkali metal, an alkaline earth metal, a transition metal, and arare-earth metal. The catalyst may be in the form of a honeycomb, packedbed, or fluidized bed.

Although other OCM catalysts can be disposed in at least a portion ofthe OCM reactors 102, in some preferred embodiments, at least a portionof the OCM catalyst in at least a portion of the OCM reactor 102 caninclude one or more OCM catalysts and/or nanostructure-based OCMcatalyst compositions, forms and formulations described in, for example,U.S. Patent Publication Nos. 2012/0041246, 2013/0023709, 2013/0158322,2013/0165728, and pending U.S. application Ser. No. 13/901,309 (filedMay 23, 2013) and 61/794,486 (filed Mar. 15, 2013), each of which isentirely incorporated herein by reference. Using one or morenanostructure-based OCM catalysts within the OCM reactor 102, theselectivity of the catalyst in converting methane to desirable C₂₊compounds can be about 10% or greater; about 20% or greater; about 30%or greater; about 40% or greater; about 50% or greater; about 60% orgreater; about 65% or greater; about 70% or greater; about 75% orgreater; about 80% or greater; or about 90% or greater.

In the OCM reactor 102, methane and O₂ are converted to C₂₊ compoundsthrough an OCM reaction. The OCM reaction (e.g., 2CH₄+O₂→C₂H₄+2H₂O) isexothermic (ΔH=−67 kcals/mole) and may require substantially hightemperatures (e.g., temperature greater than 700° C.). As a consequence,the OCM reactor 102 can be sized, configured, and/or selected based uponthe need to dissipate the heat generated by the OCM reaction. In someembodiments, multiple, tubular, fixed bed reactors can be arranged inparallel to facilitate heat removal. At least a portion of the heatgenerated within the OCM reactor 102 can be recovered, for example theheat can be used to generate high temperature and/or pressure steam.Where co-located with processes requiring a heat input, at least aportion of the heat generated within the OCM reactor 102 may betransferred, for example, using a heat transfer fluid, to the co-locatedprocesses. Where no additional use exists for the heat generated withinthe OCM reactor 102, the heat can be released to the environment, forexample, using a cooling tower or similar evaporative cooling device.OCM reactor systems useful in the context of the present invention mayinclude those described in, for example, U.S. patent application Ser.No. 13/900,898 (filed May 23, 2013), which is incorporated herein byreference in its entirety for all purposes.

As described above, in certain aspects, a mixer device or system isprovided coupled to or integrated with an OCM reactor or reactor system.Such mixers are described in greater detail below.

In some embodiments, two or more different reactant streams are mixedrapidly and sufficiently for carrying out a reaction involving the twoor more streams. In some cases, mixing will be substantially completelywithin a rapid timeframe within the mixer systems and devices describedherein.

In some cases, two or more gaseous streams can be mixed in a mixerwithin a narrow window of time targeted to be less than the time inwhich autoignition may occur at the temperatures and pressures of themixed gas streams. Such narrow window of time can be selected such thatthe streams are mixed before any OCM reaction has commenced. In someembodiments, the mixing time is no longer than the maximum residencetime before auto-ignition occurs. The mixing time can be less than 99%,95%, 90%, 80%, 70%, 60% or even less than 50% of the maximum residencetime. Each and all portions of the mixed stream can spend nearly therequisite amount of time in a mixing zone of a mixer or reactor that isconfigured to effect mixing. If the reacting mixture spends more time,then undesired reactions, sometimes irreversible, may take place, whichmay generate undesired products and possibly impede or prevent theformation of the desired products. Such undesired reactions may generatea greater proportion of non-C₂₊ impurities than C₂₊ compounds, which maynot be desirable.

In some situations, in order for the optimal residence time to beachieved by each portion of the mixing stream, the distribution of theresidence times in the mixing zone can be substantially narrow so as toreduce the possibility for even a small portion of the stream to spendless or more than the allowed time in the mixing area. Such phenomenoncan occur if recirculation and/or stagnant areas are formed due to thedesign of the mixer itself. For example, if the mixing device is aperforated cylinder located in the mainstream of the larger gaseousstream, the cylinder itself can produce significant recirculation zonesin the areas immediately downstream, thus generating a wide right tailin the statistical distribution of residence times. Systems and methodsof the present disclosure can advantageously avoid such problems.

The present disclosure provides systems and methods for mixing reactantspecies (e.g., methane and O₂) prior to or during reaction to form C₂₊compounds, such as by an OCM reaction. In some examples, i) two or moregaseous streams are mixed together within a certain time frame and witha given (e.g., minimum) degree of uniformity, and ii) the resultingmixed stream affords a limited overall residence time and a narrowdistribution of residence times before operating conditions of thestream are significantly affected by undesired chemical reactions. Priorto or during mixing, reactant species may be preheated.

A mixer can be integrated with an OCM reactor or separate from the OCMreactor, such as a standalone mixer. FIG. 2A shows an OCM system 200comprising a methane stream 201 and an air stream (comprising O₂) 202that are each directed through heat exchangers 203 and 204, where eachof the streams 201 and 202 is preheated. Next, the streams 201 and 202are directed to a mixer 205 comprising a plurality of mixing nozzles206. The nozzles 206 can be in two-dimensional array or in concentriccircles, for example. The nozzles can each have the shape of an airfoil,as described elsewhere herein. Void space 207 between the nozzles 206can be filled with a packing material (e.g., silica) to aid inpreventing recirculation of the mixed gas.

The system 200 further comprises a catalyst bed 208 downstream of themixer 205. The catalyst bed 208 can include an OCM catalyst, asdescribed elsewhere herein. A void space 209 between the mixer 205 andcatalyst bed 208 can be unfilled, or filled with an inert medium, suchas, for example, aluminum oxide (e.g., alumina) or silicon oxide (e.g.,silica) beads. In some cases, the void space can be filled with amaterial that increases the auto ignition delay time (AIDT), for exampleby changing the heat capacity of the media and/or interacting with theinitial stage of combustion chemistry by scavenging highly reactivespecies that can act as combustion initiators. Suitable materials caninclude zirconia beads, ceramic foams, metal foams, or metal or ceramichoneycomb structures. The use of materials that increase the AIDT can beadvantageous at elevated pressures (e.g., above about 3, 5, 10, 15, 20,25, 30, 35, or 40 barg). The system 200 can include a reactor liner 210that can insulate the system 200 from the external environment. Theliner 210 can thermally insulate the mixer 205 and catalyst bed 208 fromthe external environment.

In each nozzle 206 of the mixer 205, methane and air (including oxygen)can be mixed to form a mixed stream that is directed to the catalyst bed208. In the catalyst bed 208, methane and oxygen react to form C₂₊compounds in an OCM process. The C₂₊ compounds along with othercompounds, such as unreacted methane and oxygen, are directed out of thesystem 200 in a product stream 211.

With reference to FIG. 2B, as an alternative, the void space 209 can beprecluded and the catalyst bed 208 can be directly adjacent to (and insome cases in contact with) the mixer. The nozzles 206 can eachoptionally be positioned above, immediately adjacent, or in some caseseven extend into the catalyst bed 208. In such a case, an individualnozzle 206 can be surrounded by catalyst material. In some cases, atleast 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 20%, 30%, 40%, or 50% ofthe length of an individual nozzle 206 can extend into the catalyst bed208.

In certain examples, oxygen containing gas, e.g., air, can be introducedinto the nozzle 206 at the top of the nozzle 206, and methane can beintroduced into the nozzle 206 along the side of the nozzle 206, asshown. As an alternative example, methane can be introduced into anozzle 206 at the top of the nozzle 206, and oxygen containing gas canbe introduced into the nozzle 206 along the side of the nozzle 206. Thelocation of entry along a side of the nozzle 206 can be varied toprovide optimal desired mixing, and selected to provide a given mixedgas distribution.

In some situations, the OCM system 200 is operated at a reactor inlettemperature of less than about 800° C., less than about 700° C., lessthan about 600° C., less than about 500° C., or less than about 400° C.In some embodiments, the OCM system 200 is operated at a reactor inlettemperature of at least about 800° C., at least about 700° C., at leastabout 600° C., at least about 500° C., or at least about 400° C.

In some embodiments, the OCM system 200 is operated at an inlet pressureless than about 30 bar (gauge), less than about 20 bar, less than about10 bar, less than about 9 bar, less than about 8 bar, less than about 7bar, less than about 6 bar, less than about 5 bar, less than about 4bar, less than about 3 bar, or less than about 2 bar. In some cases, theOCM system 200 is operated at an inlet pressure greater than about 30bar (gauge), greater than about 20 bar, greater than about 10 bar,greater than about 9 bar, greater than about 8 bar, greater than about 7bar, greater than about 6 bar, greater than about 5 bar, greater thanabout 4 bar, greater than about 3 bar, or greater than about 2 bar.

In some situations, the OCM system 200 is operated at and a methane tooxygen ratio that is at least about 1, at least about 2, at least about3, at least about 4, at least about 5, at least about 6, at least about7, at least about 8, at least about 9, or at least about 10.

The OCM catalyst can be operated at a peak bed temperature that is lessthan about 1100° C., less than about 1000° C., less than about 900° C.,less than about 800° C., or less than about 700° C. The OCM catalyst canbe operated at a peak bed temperature that is greater than about 1100°C., greater than about 1000° C., greater than about 900° C., greaterthan about 800° C., or greater than about 700° C. The OCM catalysttemperature may be lower at lower methane to oxygen ratios. Thetemperature change across the catalyst bed (e.g., from inlet to outlet)can scale with the methane to oxygen ratio. In some cases, a lowermethane to oxygen ration can effect a larger temperature change acrossthe catalyst bed.

FIG. 3A shows an OCM system 300 comprising a methane stream 301 and anair stream (comprising O₂) 302 that are each directed through heatexchangers 303 and 304, respectively, where each of the streams 301 and302 is preheated. In an example, the methane stream 301 is preheated toa temperature between about 450° C. and 650° C., and the air stream ispreheated to a temperature between about 450° C. and about 650° C. Next,the methane stream 301 is directed to a mixer of the OCM system 300. Themixer includes a feed flow distributor 305. The feed flow distributor305 can be, for example, in the form of a showerhead, which can includea plurality of concentric holes. The feed flow distributor 305 canprovide a uniform flow of methane. The air stream 302 is directed intothe OCM system 300 to an air distributor 306, which provides streams ofair upward towards the feed flow distributor and downward towards acatalyst bed 307. The catalyst bed 307 can include an OCM catalyst, asdescribed elsewhere herein. As used throughout, references to “air”,“air streams”, and the like should be understood to include enrichedair, oxygen, or any other oxidant that can be used to carry out an OCMreaction. Air is but one example of an oxygen source for OCM. When O₂ isused as the oxidant, the air stream (i.e., O₂) can be pre-heated tobetween about 150° C. and 350° C., or between about 200° C. and 250° C.,inlet temperature.

The air distributor 306 can be a hollow device that includes a chamberin fluid communication with a plurality of fluid flow paths that leadfrom the chamber to a location external to the air distributor 306. Inan example, the air distributor is a hollow tube that includes aplurality of holes along a length of the tube. In another example, theair distributor is a hollow plate (e.g., circular plate) with aplurality of holes. In either example, some of the holes can pointtowards the feed flow distributor 305 and other holes can point towardsthe catalyst bed 307.

The system 300 can include a reactor liner 308 that can insulate thesystem 300 from the external environment. The liner 308 can thermallyinsulate the distributors 305 and 306, and catalyst bed 307, from theexternal environment.

In the catalyst bed 307, methane and oxygen react to form C₂₊ compoundsin an OCM process. The C₂₊ compounds along with other compounds, such asunreacted methane and oxygen, are directed out of the system 300 in aproduct stream 309.

In the example of FIG. 3A, the air distributor 306 is disposed at alocation between the feed flow distributor 305 and the catalyst bed 307.As an alternative, the air distributor 306 can be disposed in an inertpacking medium or the catalyst bed 307. In FIG. 3B, the air distributor306 is situated in an inert packing medium 310 that is situated betweenthe feed flow distributor 305 and the catalyst bed 307. The inertpacking medium 310 can include, for example, aluminum oxide (e.g.,alumina) or silicon oxide (e.g., silica) beads. In FIG. 3C, the airdistributor 306 is situated in the catalyst bed 307. In the illustratedexample, the air distributor 306 is situated in the catalyst bed 307 ata location that is at or adjacent to the point at which methane entersthe catalyst bed. However, other locations may be employed. For example,the air distributor 306 can be situated at a location that is at or atleast about 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% of thelength (i.e., from top to bottom in the plane of the figure) of thecatalyst bed 307.

In some embodiments, mixers include one or more airfoils. FIGS. 4A and4B show an OCM system 400 comprising a mixer (or injector) 401 and a gasdistribution manifold 402 adjacent to the mixer 401. FIG. 4Bschematically illustrates a cross-section of the system 400, taken alongline 4B-4B in FIG. 4A. The mixer 401 comprises a plurality of ribs 403that are airfoils. An upstream portion of each of the ribs 403 has alarger cross-section than a downstream portion of each of the ribs 403.The ribs 403 can be hollow.

In some embodiments, a mixer is capable of mixing a first gas (e.g.,CH₄) and a second gas (e.g., O₂) within about 1000 ms, 500 ms, 400 ms,300 ms, 200 ms, 100 ms, 50 ms, or 10 ms. The mixer can include aplurality of manifolds, such as airfoil-shaped manifolds, distributedacross a fluid flow path.

In FIGS. 4A and 4B, a first fluid stream is directed into the gasdistribution manifold 402 at a first inlet 404. A second fluid stream isdirected into the mixer 401 at a second inlet 405 (along the directionof the arrows (i.e., upstream do downstream), at which point the secondfluid stream is directed to along a fluid flow path 406 to the ribs 403.The fluid flow path 406 can be a chamber that is in fluid communicationwith the inlet 405 and the ribs 403. In some examples, the first fluidstream comprises a hydrocarbon (e.g., methane) and the second fluidstream comprises an oxidizing agent. In an example, the second fluidstream is air and the oxidizing agent is O₂.

The system 400 further comprises an OCM reactor 407 downstream of themixer 401. The ribs 403 are situated along a fluid flow path that leadsfrom the inlet 404 to the OCM reactor 407. During use, the first fluidstream enters the system 400 at the inlet 404 and is directed to the gasdistribution manifold 402. The second fluid stream enters the system 400at the inlet 405 and is directed along the fluid flow path 406 to theribs 403. As the second fluid stream is directed along the fluid flowpath, heat from the OCM reactor 407 can heat the second fluid stream.The heated fluid stream enters the ribs 403 and is directed out of theribs to mix with the first fluid stream that is directed towards the OCMreactor 407 from the gas distribution manifold 402.

The mixer 401 can be close coupled with the OCM reactor 407. In somecases, the OCM reactor 407 includes a catalyst that is included in aspace between the ribs 403. The OCM reactor 407 can have various shapesand sizes. The OCM reactor 407 can have a cross-section that iscircular, oval, triangular, square, rectangular, pentagonal, hexagonalor any partial shape and/or combination thereof. In an example, the OCMreactor 407 is cylindrical in shape. In some examples, the OCM reactor407 has a diameter between about 1 foot and 100 feet, or 5 feet and 50feet, or 10 feet and 20 feet. In an example, the OCM reactor 407 has adiameter that is about 12 feet.

The OCM reactor 407 can include a liner 408 that can be formed of arefractory material. Examples of refractory materials include the oxidesof aluminum (e.g., alumina), silicon (e.g., silica), zirconium (e.g.,zirconia) and magnesium (e.g., magnesia), calcium (e.g., lime) andcombinations thereof. Other examples of refractory materials includebinary compounds, such as tungsten carbide, boron nitride, siliconcarbide or hafnium carbide, and ternary compounds, such as tantalumhafnium carbide. Refractory material can be coated and/or doped withrare earth elements or oxides, or other basic alkaline earth and/oralkali metals. This may aid in preventing coking. OCM catalyst nanowiresmay also be used to coat refractory material to prevent coking. Theliner 408 can have a thickness from about 0.5 inches and 24 inches, or 1inch and 12 inches, or 3 inches and 9 inches. In an example, the liner408 has a thickness of about 6 inches.

The inlets 404 and 405 can have various shapes and sizes. The inlet 405can have cross-section that is circular, oval, triangular, square,rectangular, pentagonal, hexagonal or any partial shape and/orcombination thereof. In some examples, the inlet 404 has a diameterbetween about 10 inches and 100 inches, or 20 inches and 80 inches, or40 inches and 60 inches. In an example, the inlet 404 has a diameterthat is about 56 inches. In some examples, the inlet 405 has a diameterbetween about 1 inch and 50 inches, or 10 inches and 30 inches, or 15inches and 20 inches. In an example, the inlet 405 has a diameter thatis about 18 inches.

Each of the ribs 403 can be an airfoil mixer that is configured to bringthe second fluid stream in contact with the first fluid stream. This canprovide for uniform mixing. Each of the ribs 403 can include one or moreopenings that are in fluid communication with a fluid flow path leadingfrom the inlet 404 to the OCM reactor 407. In some examples, each of theribs 403 has an opening on a top or bottom portion of a rib (withrespect to the plane of the figure) and/or on opposing sideportions—i.e., along a direction that is orthogonal to the direction offluid flow from the inlet 404 to the OCM reactor 407. By introducing thesecond fluid stream to the first fluid stream prior to the OCM reactor407, the ribs can enable mixing of the first and second fluid streamsprior to an OCM reaction in the OCM reactor 407.

In some cases, the point along a given rib 403 at which the second fluidstream is introduced to the first fluid stream, as well as the fluidproperties of the respective streams (e.g., pressure, flow rate and/ortemperature), is selected such that the auto-ignition (e.g., automaticcombustion or partial combustion of methane) prior to the OCM reactor407 is minimized, if not eliminated. This can help ensure that reactionbetween a hydrocarbon (e.g., methane) and an oxidizing agent (e.g.,oxygen) occurs in the OCM reactor 407 to yield C₂₊ compounds, and helpsreduce, if not eliminate, unwanted reactions, such as the partial orcomplete combustion of the hydrocarbon. In some examples, the secondstream is introduced to the first stream at the top of each of the ribs403.

A rib can be a blade that is in the shape of an airfoil. FIG. 5 shows ablade 501 that may be employed for use as a rib. In some examples, theblade can have a width (the widest portion, ‘W’) from about 0.5 inchesto 10 inches, and a length from about 0.5 ft. to 10 ft. The blade 501can be part of a mixer upstream of an OCM reactor. The mixer can beintegrated with the OCM reactor. The mixer and OCM reactor can beintegrated with a heat exchanger (see below). During operation of an OCMsystem having the blade 501, a first fluid stream is directed along afluid flow path 502. The first fluid stream can include a hydrocarbon,such as methane. A second fluid stream 503 is directed out of the blade501 through openings 504 on opposing sides of the surfaces of the blade501. The openings 504 can be holes or slits, for example. The secondfluid stream 503 can include an oxidizing agent, such as oxygen (O2). Inan example, the second fluid stream 503 includes air. The second fluidstream can include a mixture of oxygen and methane.

The openings 504 can be on the sides of the blade 501. As an alternativeor in addition to, the openings 504 can be on a top and bottom portionof the blade (with respect to the plane of the figure). The blade 501can have at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, or 100openings, which can have various sizes and configurations. For example,the openings 504 can be holes or slits. The openings can be disposedside-by-side along the length of the blade 501 (i.e., along an axisorthogonal to the width of the blade (‘W’) and in the plane of thefigure), or side by side along a thickness of the blade 501 (i.e., alongan axis orthogonal to the width of the blade and orthogonal to the planeof the figure).

The mixer can provide rapid and complete mixing of two or more gasstreams. Additionally, the airfoil shape can help minimize, if noteliminate, stagnant or re-circulation zones in a mixing zone downstreamof the mixer. This allows for every portion of the mixed stream to spendthe same amount of time within the mixing zone, thus leading to a verynarrow and controlled distribution of the residence times in the mixingzone itself.

FIG. 6 is a plot from a computational fluid dynamics (CFD) analysis ofan airfoil-shaped mixer in fluid communication with an OCM reactor. Afirst gas stream 601 is a methane-containing stream (0% oxygen). Asecond gas stream 602 is an air stream containing about 21% oxygen (O₂).The second gas stream 602 is provided to the first gas stream viaairfoil-shaped blades 603. A third gas stream 604 is a mixed streamcomprising methane from the first gas stream 601 and oxygen from thesecond gas stream 602. Use of the airfoil-shaped blades 603advantageously provides for the absence of stagnant (or re-circulating)zones in the third gas stream 604 downstream of the blades 603. The flowprofile in the third gas stream 604 also displays compositionaluniformity immediately after the blades 603.

The present disclosure also provides a reactor system for performingoxidative coupling of methane to generate C₂₊ compounds, comprising amixer capable of mixing a first gas stream comprising methane with asecond gas stream comprising oxygen to provide a third gas stream, and acatalyst that performs an OCM reaction using the third gas stream toproduce a product stream comprising one or more C₂₊ compounds. Duringreaction, the OCM reaction liberates heat. The system further comprisesone or more flow reversal pipes in fluid communication with the mixerand at least partially surrounded by the catalyst. The flow reversalpipes comprise an inner pipe circumscribed by an outer pipe along atleast a portion of the length of the inner pipe. The inner pipe is openat both ends and the outer pipe is closed at an end that is surroundedby the catalyst. The flow reversal pipes are configured to transfer heatfrom the catalyst to the second gas stream during flow along the innerpipe and/or a space between the inner pipe and outer pipe.

In some situations, the second gas stream (i) flows through the innerpipe into the catalyst along a first direction and (ii) flows in a spacebetween the inner pipe and outer pipe out of the catalyst along a seconddirection that is substantially opposite to the first direction. As analternative, the second gas stream (i) flows through a space between theinner pipe and outer pipe and into the catalyst along a first directionand (ii) flows in the inner pipe and out of the catalyst along a seconddirection that is substantially opposite to the first direction.

The use of airfoil-shaped manifolds can enable cross-mixing of onestream into another stream, which can aid in providing a high degree ofuniformity in a substantially compact space. Spacing, size and number ofthe airfoil-shaped manifolds can be optimized on a case-by-case basis toproduce the desired or otherwise predetermined uniformity at the outletof the mixer while maintaining the height of the manifold within themaximum allowable height, to minimize the time spent by the mixed streamin the mixer zone.

In some cases, a flow distributor (e.g., a porous packed catalyst bed)is used in conjunction with the manifold to achieve no or limited flowrecirculation as captured by negative velocities (e.g., against bulk offlow). The mixing device is not limited to the manifolds alone. In somecases, a flow straightener, an air distribution manifold, packing (e.g.,touching the air foils underneath the manifold), and/or an expansioncone with a specified angle are used. In some cases, the manifold isclosely coupled with a flow control element such as a metal or ceramicfoam, a bed of packed particles or other porous media suppressing flowrecirculation in a zone downstream of the manifold.

The present disclosure also provides for a reactor system using one ormore bypass reactor channels or legs. A bypass channel or leg can bypassa section of a reactor or catalyst bed. Use of a bypass channel canallow a portion of a feed stream to bypass a section of a reactor orcatalyst bed, rather than transiting the entire reactor or bed. A bypasschannel can be internal to the reactor or catalyst bed. For example, abypass channel can comprise a region of catalytically inert materialwithin a catalyst bed. A bypass channel can be external to the reactoror catalyst bed. For example, a bypass can comprise a pipe or otherconduit which directs a portion of feed stream into a catalyst bed at apoint downstream of a section of the catalyst bed. Use of a bypasschannel or leg can decrease the feed linear flow rate at the front endof the catalyst bed compared to the feed linear flow rate at the back ofthe catalyst bed. Light off temperature and inlet temperature underoperating conditions can both be dependent on the linear flow ratethrough the catalyst. Using a bypass leg can result in a lower light offtemperature. Using a bypass leg can result in a lower inlet temperature.Using a bypass leg can result in a lower extinction temperature. Lowerinlet temperature can result in lower risk of premature, non-catalyzedfeed reaction. Lower inlet temperature can result in greater conversionacross a catalyst bed. Using a bypass leg can result in higherselectivity. Using a bypass leg can preserve a greater amount of higherhydrocarbons from a feed stream in a product stream. A reactor systemcan comprise 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or more bypass legs orchannels. The reactor or catalyst bed can comprise a mixing section formixing product from a first section of catalyst bed with feed materialfrom a bypass. The mixing section can mix material from the initialsection of the reactor or catalyst bed with feed material from thebypass channel. The effect of a bypass channel can be created by usingmultiple reactors with refractory lining between them to preserve thetemperature rise from partial conversion of the feed in the firstsection.

A partial bypass leg can be employed for the use of wet natural gas. Areactor can comprise a first section of a reactor catalyst bed (e.g.,OCM bed) and a second section of a reactor or catalyst bed (e.g., OCMbed). The reactor or catalyst bed can comprise a mixing section formixing product from a first section of catalyst bed with feed materialfrom a bypass. Prior to entering a reactor feed, a methane source stream(e.g., natural gas stream) can be dried in a dryer (e.g., pressure swingadsorption (PSA) dryer). The dryer can produce a dry methane sourcestream (e.g., natural gas stream) and a wet methane source stream (e.g.,natural gas stream). Wet methane source can be fed into a reactor orcatalyst bed via a bypass, bypassing a first section of the reactor bed.A wet methane source stream can comprise higher hydrocarbons. Forexample, at about a 15% to 30% methane rejection rate from a dryer, awet methane source stream can comprise about five times higherconcentration of higher hydrocarbons than the inlet methane sourcestream. Higher hydrocarbons in a wet methane source stream can bypass aportion of the reactor bed, being injected into a section of reactorwhere O₂ is reduced significantly and intermediate temperature is high,improving the reaction of such higher hydrocarbons. Such a process canbe combined with a selective olefin removal sorption unit to close theloop and allow recycling of hydrocarbons. Such a process can be combinedwith in bed cracking with supplemental O₂.

As described in the present disclosure, a reactor with OCM feed flowsplitting and a method for reaction of a fraction of the oxygen in anOCM reactor sub-section can be beneficial. For example, the reactors andmethods described herein can aid in creating greater control of oxygenusage and temperature rise through the reactor. In particular, combiningan OCM product stream with cooler unreacted feed can have severalbenefits.

A first benefit can be increasing the operating range of the reactorsystem for lower gas inlet temperatures. This can be achieved by usinglonger residence times and lower gas linear velocities in the OCMreactor subsection and processing a fraction of the oxygen beforeremixing its effluent to the remainder of the OCM reactor system feed.The reactor extinction temperature in the highly exothermic OCM reactioncan be strongly depressed by increasing the reactor residence time andlowering gas linear velocities.

A reduced inlet gas temperature in adiabatic OCM reactor systems can bebeneficial for increasing per pass conversion and reducing thelikelihood of premature auto-ignition of the feed mixture. Prevention ofauto-ignition can be more challenging with increased pressure ofoperation.

Another benefit of the reactors and methods described herein can bereducing exposure of higher hydrocarbons included in the OCM feed gas tointermediate reaction temperatures (e.g., in the range of 450° C. to650° C.). At these intermediate operating temperatures, higher alkanesor alkenes can be (preferentially) combusted to CO₂ and water. However,at higher temperatures most of these desirable molecules are leftintact.

Reducing combustion of desirable molecules in the feed can be importantfor multistage OCM reactor trains, as propylene and ethylene in theeffluent of the upstream reactor(s) have to go through downstreamreactors after being mixed with additional oxygen. Reducing combustioncan also be desirable when processing wet natural gas feeds (e.g.,natural gas having C₂₊ compounds). Avoiding combustion at the inlet ofthe OCM catalyst bed can enable the use of the higher hydrocarbons inthe feed for cracking downstream of the OCM bed.

If the bypass region of the reactor and the split reaction section ofthe reactor are in good thermal contact, there can be an additionalbenefit of controlling the catalyst temperature and improved catalystlife.

A reactor system can be designed to employ chemical looping. Chemicallooping can comprise the transfer of material, such as catalyst bedmaterial, from one catalyst bed to another. For example, a reactorsystem can comprise two reactor beds, wherein a bed material is oxidizedin a first bed, then transferred to a second bed and used as an oxygensource for a reaction or other process, thereby becoming reduced andready for oxidation in the first bed again. In this way, catalyst bedmaterial can serve as an oxygen carrier. The steps of oxidation of bedmaterial, transfer of bed material from a first bed to a second bed,reaction with reduction of bed material, and transfer of bed materialfrom the second bed back to the first bed can be repeated as often or asfrequently as needed. This design can be extended to systems comprisingmore than two beds, such as systems with 3, 4, 5, 6, 7, 8, 9, 10, ormore beds. In some cases, oxygen provided by oxidized bed material canbe the predominant source of oxygen for a reaction. In some cases,oxygen provided by oxidized bed material can be the sole source ofoxygen for a reaction. Providing oxygen via an oxygen carrier ratherthan from molecular oxygen can result in reduced amounts of molecularoxygen present during a reaction, such as an OCM reaction. Reducedamounts of molecular oxygen can result in lower CO₂ yield from thereaction, as well as increased selectivity to C₂₊ products. A reactorbed can comprise a fluidized bed. Oxygen carrier materials can comprisebut are not limited to Ni₂O₃, Al₂O₃, CeO₂, MnO₂, SiO₂, perovskites,lanthanides, actinides, mixed oxides, and combinations thereof.

The present disclosure also provides for an integrated OCM fluid bedwith partial reactive air separation. OCM can be used to consume oxygen(e.g., O₂) from air in one section of a reactor (e.g., a fluidized bedreactor), and O* regenerated catalyst can be reacted with natural gas oranother methane source to produce olefins in a second section of areactor. The reactor sections can be adjacent to each other. The reactorsections can be physically separated and have a means to move catalystparticles between sections. The bed material can have a fraction whichmoves counter to the gas flow. This movement can allow for carryingadsorbed species or chemical potential between reactor sections withoutmixing the reducing and oxidizing streams. Steam can be injected toreduce the N₂ content of a resulting OCM product stream. The pressure ofoutlet flows can be controlled to achieve a specific N₂ separation.Minimized gas linear velocity can be maintained in each reactor sectionto enable circulation of solid material. Different reactor sections canhave different geometric parameters, such as tube diameter, which can beused to achieve a particular linear velocity profile.

A reactor system can comprise beta-SiC catalyst support. Beta-SiC can beused as a support for OCM catalyst formulations. Use of beta-SiC as acatalyst support can allow well-controlled heat transfer from catalystactive sites to lower hot spots on catalytic active sites. Use ofbeta-SiC as a catalyst support can improve catalyst life. Use ofbeta-SiC as a catalyst support can reduce or prevent loss of catalystcomponents into the gas phase. Use of beta-SiC as a catalyst support canallow use of smaller amounts of catalyst; for example, 25%-33% of OCMcatalyst on beta-SiC can be sufficient for an OCM reaction. Beta-SiCcatalyst supports can be stable to boiling in strong acids and bases,allowing recovery of catalyst components from the catalyst support.Active catalyst materials that may be deposited on beta-SiC catalystsupports may be as described herein, including materials described in,for example, U.S. Patent Application Nos. 2012/0041246, 2013/0023079,2013/165728, and U.S. patent application Ser. Nos. 13/936,783 and13/936,870 (both filed Jul. 8, 2013), each of which is entirelyincorporated herein by reference.

A reactor system can employ a graded catalyst concentration throughout acatalyst bed. For example, the top of a catalyst bed can comprise a pureOCM catalyst composition while a portion of the outlet sections of thebed can comprise an impregnated SiC-based catalyst, a catalyst supportwith a lower concentration of OCM catalyst, or a SiC catalyst supportwithout any supported catalyst. A graded catalyst concentration canresult in less catalyst usage in a reactor bed. A graded catalystconcentration can enhance catalyst selectivity. A graded catalystconcentration can improve catalyst life. The catalyst concentration canvary (e.g., along the direction of fluid flow through the bed) by atleast about 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%,65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, 100%, 150%, 200%,250%, 300%, 350%, 400%, 450%, 500%, 550%, 600%, 650%, 700%, 750%, 800%,850%, 900%, 950%, or 1000% across the catalyst bed.

The present disclosure provides for a reactor system employing a tubularbed design. Large radial temperature gradients can be generated andmaintained in a tubular reactor as cooling is limited by heat transportinside the tube. The temperature profile inside the tube can be drivenby the non-linear increase in catalyst activity with temperature and theeffect of local O₂ concentration. Use of a single catalyst charge canresult in a single hot zone radially centered in or near the middle ofthe tube, with an increase in temperature followed by a drop in O₂levels resulting in a drop in temperature.

A tubular bed reactor can comprise multiple zones. Active catalyst canbe distributed in layers or zones separated by inert material (e.g.,inert packing). Inert material can provide gas mixing. The reactionmixture can cool down between active zones, allowing use of a largercatalyst bed volume compared to a homogenous packing of active catalyst.Mixing can occur between zones, for example by a ceramic orceramic-lined metal Sulzer mixer or by a tab mixer.

A tubular bed reactor can comprise semi-multistage adiabatic design.Large longitudinal temperature gradients can be generated through areactor bed, with peak temperature capped by the adiabatic reactiontemperature. Active catalyst can be distributed in layers or zonesseparated by inert material (e.g., inert packing). Inert material canprovide gas mixing. The inlet temperature of each stage can becontrolled to a low enough temperature to enable addition ofsupplemental air to continue the reaction. Air can be introduced ininert packing sections between catalytically active zones.

Inert packing sections can incorporate a solid core to improve heattransfer to the wall. Use of a solid core can promote a flattertemperature profile at the inlet of active catalyst zones. Tubularreactors can comprise a radial catalyst composition gradient. Forexample, the reactor tube can be packed with mostly inert material nearthe tube wall and with a charge of mostly active material in the tubecenter. A non-porous insulation liner can be used in place of an outerlayer of inert packing. Radial tube composition gradients can promotebypass of material and extend the length of tube used to perform thereaction. Radial tube composition gradients can reduce the proportion ofreaction occurring at intermediate temperatures. Radial packing can beachieved using a cylindrical guide to separate bed zones during packing.Different guide shapes can be used in different sections of the reactortube. Different zone shapes can provide different flow resistances.Different flow resistances can equalize flow resistance through thereactor tube in the presence of a large radial temperature gradient.Flow can be fed down the center of the reactor tube and out through theperimeter space, or vice versa.

The catalyst can be organized or arranged in the reactor (i.e., packed)in various geometries that can lead to various advantages. FIG. 29Ashows a standard bed packing geometry where a catalyst bed 2900 ispacked over a layer of inert material 2905. Reactants flow into thereactor 2910 and are converted to products, which flow out of thereactor 2915. Alternate bed packing strategies are shown in FIG.29B-29D.

The bed packing in FIG. 29B uses a combination of catalytically activeand catalytically inert packed materials to modulate the reactortemperature profile. Here, regions of catalyst 2920 are interspersed andalternated with regions of inert material 2925 in the packed bed. Thisconfiguration can be useful for moderating the temperature of the activecatalyst bed by increasing the volume into which the reaction is carriedout and heat produced. With this increase of volume, the surface area ofthe tube in contact with the (heat generating) reaction volumeincreases, enabling improved control of heat removal from the system.Using a band of catalytically inert packing as shown in FIG. 29B can bebetter than simply diluting the all catalyst bed with inert material(i.e., mixing the catalyst and the inert material) because a largeradial gradient within the tube can be desirable to increase the averagebed operating temperature. Addition of axial bands has minimal impact onthe radial temperature gradient, while allowing to spread the heatreleased by the reaction axially.

The bed packing in FIG. 29C uses a combination of a catalyst bed 2930and an inert material 2935 that is essentially non-porous or has a highflow resistance. The catalyst bed can surround the inert material, whichcan be any shape, including wider nearer the entrance of the reactantsand narrower nearer the exit of the products. This strategy creates anuneven distribution of catalyst and gas flow across the tube section.The geometry of FIG. 29C can be useful for moderating the temperature inthe active catalyst bed by creating a gradient of gas linear velocitywithin the catalyst bed. The gradient has a higher gas flow rate at theinlet than at the outlet of the bed. This geometry also has increasedheat exchange area as the volume of the reactor that is used isincreased. The geometry of FIG. 29C can allow for flexibility in thedesign of the flow rate gradient from the inlet to the outlet of thetube. It can also be cost effective compared to varying the diameter ofthe metal tube by welding multiple tube sections together.

The bed packing shown in FIG. 29D uses a combination of a catalystpacked bed 2940 and a thermally insulating material 2945. This packinggeometry can increase the residence time of the process gas at hightemperature once the oxygen in the feed is depleted. This can bedesirable because of the endothermic cracking of ethane to ethylenetaking place in the back end of OCM reactor. Adding thermal insulationat a location where most of the oxygen is depleted increases theethylene yield of the tubular reactor.

Pre-Heating Devices, Systems and Methods

Another aspect of the present disclosures provides heating devices,systems and methods. Such devices, systems and methods may be employedfor use in pre-heating reactant streams prior to an OCM reaction.Pre-heating devices, systems and methods of the present disclosure canbe used separately or in conjunction with other pre-conditioningapproaches of the present disclosure, such as mixing. For example, apre-heater can be integrated with a mixer. As another example, apre-heater can be separate from a mixer and situated upstream ordownstream of the mixer but situated prior to an OCM reactor.

In some embodiments, streams comprising an oxidizing agent (e.g., O₂,which may be provided by way of air) and/or methane are heated byreaction heat prior to being mixed. This can advantageously reduce theamount of reaction heat that is lost as waste heat, which can decreasethe amount of energy that is used in external heat exchangers topre-heat the streams.

For example, an air stream or methane stream can be heated by heat froman OCM reactor. As another example, a mixed stream comprising air andmethane is heated by heat from an OCM reactor. The air and/or methanestream can be directed along a location that is in thermal communicationwith a catalyst bed to provide heat to the air and/or methane streamprior to mixing or an OCM reaction to generate C₂₊ compounds. In someexamples, the air and/or methane stream are directed to a heat exchangerthat is integrated with the OCM reactor, where at least a portion of theheat from the OCM reaction is transferred to the air and/or methanestream.

In some embodiments, a system for performing an OCM reaction to generateC₂₊ compounds comprises an OCM reactor comprising an OCM catalyst thatfacilitates the OCM reaction to generate the C₂₊ compounds, and aninjector comprising a fluid flow conduit that directs a first gas streamthrough at least a portion of the OCM reactor to one or more openingsthat are in fluid communication with the OCM reactor. The fluid flowconduit is in thermal communication with the OCM reactor, and the firstgas stream comprises one of methane and an oxidizing agent. In someexamples, the oxidizing agent includes oxygen (O₂). The system furthercomprises a gas distribution manifold comprising one or more openingsthat are in fluid communication with the one or more openings of theinjector and the OCM reactor. The gas distribution manifold directs asecond gas stream into the OCM reactor. The second gas stream comprisesthe other of methane and the oxidizing agent.

An OCM reactor can be integrated with a heat exchanger, which can enablereactant streams to be preheated by heat liberated from a reactor tooptimize a downstream reaction, such as an OCM reaction. For example, astream comprising an oxidizing agent (e.g., O₂), such as an air stream,can be heated with a stream comprising a hydrocarbon stream (e.g.,methane) prior to mixing. The mixed stream can then be directed to theOCM reactor, as described above or elsewhere herein.

A mixture of methane and oxygen can be reactive above a giventemperature. The auto-ignition temperature of methane in air is about580° C. at atmospheric pressure. Under such conditions, bringing methanein contact with oxygen at such elevated temperature may lead topremature reaction, such as partial or complete combustion, leading topotentially undesirable products, such as CO and CO₂. However, it maynot be desirable to decrease the temperature of a methane and/or O₂stream (e.g., below the auto-ignition temperature) as this may decreasethe overall conversion in an OCM process.

The present disclosure provides various approaches for reducing, if noteliminating the auto-ignition of methane. In some cases, the time thatmethane is in contact with O₂ is reduced while the temperature of themethane and/or O₂ streams is maintained at a requisite level to effect agiven degree of conversion. The light off temperature for an OCMreaction can be a function of linear flow rate through the OCM reactor(e.g., catalyst bed). Similarly, minimal inlet temperature underoperating conditions may be affected by the linear flow rate though theOCM reactor.

In some embodiments, an inlet section is used to process a fraction ofthe inlet gas feed (e.g., less than 33%) at reduced local flow rate andinject the reaction product in a second section of the OCM reactor whereunreacted bypass feed will contact a hotter reacted product stream(e.g., stream containing C₂₊ compounds), such as in a counter flowfashion. The hotter product stream can be used to promote the OCMreaction by increasing the OCM reactor temperature relative to thereactor feed inlet. In some examples, an artificially created bypasschannel is provided through at least a portion of an OCM reactor, whichcan decrease the feed linear flow rate in the front end of the OCMreactor compared to the feed linear flow rate in the back of the OCMreactor.

OCM systems of the disclosure can be integrated with heat exchangers,which can enable heat liberated in an OCM reaction to be used to heat(or preheat) methane and/or an oxidizing agent (e.g., 0, which may beprovided by air) prior to an OCM reaction. In some embodiments, heatgenerated from an OCM reaction is used to increase a reactor inlet gastemperature. FIG. 7A shows an OCM system 700 comprising a methane stream701 and an air stream (comprising O₂) 702 that are each directed throughheat exchangers 703 and 704, respectively, where each of the streams 701and 702 is preheated. Next, the methane stream 701 is directed to a feedflow distributor 705 of the OCM system 700. The feed flow distributor705 can be, for example, in the form of a showerhead, which can includea plurality of concentric holes. The feed flow distributor 705 canprovide a uniform flow of methane. The air stream 702 is directed intothe OCM system 700 to an air distributor 706, which provides streams ofair upward towards the feed flow distributor and downward towards acatalyst bed 707. The catalyst bed 707 can include an OCM catalyst, asdescribed elsewhere herein. The air stream 702 is directed to the airdistributor 706 along a conduit 708 that includes a fluid flow that isin thermal communication with the catalyst bed 707. The conduit 708 canbe a tube or channel that can be isolated from the catalyst bed 707. Insome cases, multiple conduits 708 in fluid communication with the airdistributor 706 can be used.

The dimensions of the conduit 708 can be selected to provide fluid flowproperties that provide for preheating and provide flow characteristicsthat may be optimized for the OCM reaction. For instance, the length ofthe conduit 708 in the catalyst bed 707 can be selected such that theresidence time of air (or other fluid) is sufficient to providerequisite preheating.

The air distributor 706 can be a hollow device that includes a chamberin fluid communication with a plurality of fluid flow paths that leadfrom the chamber to a location external to the air distributor 706. Theair distributor 706 can be as described above or elsewhere herein, e.g.,in the context of FIGS. 3A-3C.

The system 700 can include a reactor liner 709 that can insulate thesystem 700 from the external environment. The liner 709 can thermallyinsulate the distributors 705 and 706, and catalyst bed 707, from theexternal environment.

In the catalyst bed 707, methane and oxygen react to form C₂₊ compoundsin an OCM process. The C₂₊ compounds along with other compounds, such asunreacted methane and oxygen, are directed out of the system 700 in aproduct stream 710.

In the example of FIG. 7A, the air distributor 706 is disposed in aninert packing medium 711. The inert packing medium 711 can include, forexample, aluminum oxide (e.g., alumina) or silicon oxide (e.g., silica)beads. As an alternative, the air distributor 706 can be disposed at alocation between the feed flow distributor 705 and the catalyst bed 707,or within the catalyst bed 707. In FIG. 7B, the air distributor 706 issituated in the catalyst bed 707. The air distributor 706 is situated inthe catalyst bed 707 at a location that is at or adjacent to the pointat which methane enters the catalyst bed. However, other locations maybe employed. For example, the air distributor 706 can be situated at alocation that is at or at least about 5%, 10%, 20%, 30%, 40%, 50%, 60%,70%, 80%, or 90% of the length (i.e., from top to bottom in the plane ofthe figure) of the catalyst bed 707.

As another alternative, the air distributor 706 can be disposed at alocation between the feed flow distributor 705 and the catalyst bed 707.For example, the air distributor 706 can be disposed in an unfilledspace between the feed flow distributor 705 and the catalyst bed 707(see, e.g., FIG. 3A and corresponding text).

During an example operation of the system 700, air is directed along theconduit 708 to the air distributor 706. As air moves along a portion ofthe conduit 708 that is situated in the catalyst bed 707, heat liberatedby the OCM process is used to pre-heat the air.

As an alternative, methane can be directed through the conduit 708 tothe distributor 706 such that methane is preheated. Air can be directedalong the stream 701 to the feed flow distributor 705.

As another alternative, multiple conduits 708 may be provided for eachof methane and air, and both methane and air are directed along separateconduits 708 through the catalyst bed 707 for heating prior to mixing.Methane and air can be mixed in a distributor, such as the distributor706 that is in fluid communication with both conduits 708. In such acase, methane and oxygen in air may be heated to a temperature that isselected to provide a given conversion during an OCM reaction. Methaneand oxygen may be precluded from contact until substantially close tothe catalyst bed 707 so as to reduce, if not eliminate, auto-ignition ofmethane.

FIG. 8 shows an OCM system 800 in which OCM reaction heat is used topreheat air. The OCM system 800 comprises a methane inlet 801 and airinlet 802. The methane inlet 801 has a temperature T1 and the air inlet802 has a temperature T2. Air from the air inlet 802 is directed along aconduit 803 where it is preheated using reaction heat (kQ). Thepreheated air is then directed to an air distributor 804. Air from theair distributor 803 is mixed with methane from the methane inlet 801 toyield a mixed stream 805, which is directed to a catalyst bed 806. Insome cases, methane from the methane inlet 801 is directed to a feedflow distributor (not shown), as described elsewhere herein. In thecatalyst bed 806, methane and oxygen (in air) undergo an OCM reaction toyield C₂₊ compounds and heat. In a heat exchanger 807, at least aportion (kQ) of the liberated heat is directed to preheat air in theconduit 803. Next, the products from the OCM process are directed out ofthe system 800 along an outlet 808. In some cases, the heat exchanger807 is integrated with the catalyst bed 806 such that the catalyst bedexchanges thermal energy with the conduit 803 directly.

FIG. 9 is a graph of temperature (y-axis, ° C.) as a function of heatexchanger efficiency (x-axis, k (unity)) for various elements the system800. A first plot 901 shows temperature as a function of heat exchangerefficiency for the outlet 508. A second plot 902 shows temperature as afunction of heat exchanger efficiency for the mixed stream 805. A thirdplot 903 shows temperature as a function of heat exchanger efficiencyfor the methane and air inlets 801 and 802, respectively.

In some cases, OCM reaction selectivity is maximized at high catalysttemperatures in the 850° C. to 950° C. range but begins to diminish attemperatures in excess of this “sweet spot” range. Under adiabaticreaction conditions, the peak catalyst temperature is proportional tothe feed oxygen concentration since the reaction is operated underoxygen limiting conditions. Thus the peak catalyst temperature can beoperated in a desired or otherwise predetermined temperature range tomaximize selectivity by setting the feed CH₄/O₂ ratio. In any commercialreaction, the desire may be to maximize product yield. For the OCMreaction, yield is selectivity multiplied by the methane conversion.Higher methane conversions can result in higher yields provided that theOCM catalyst is operated such that the OCM reaction selectivity isoptimized for given reaction conditions. The internal heat exchangerconcept may be used to operate at higher methane conversions within atoptimum selectivity. The plots show that a low efficiency heat exchanger(as may be integrated with an OCM reactor) may be employed for use in anOCM reaction. In this example, without internal heat exchange, thecatalyst temperature reaches about 1200° C., a temperature far in excessof the optimum selectivity. Employing about 31% internal heat exchange(k=0.31), the catalyst temperature is reduced to about 950° C., atemperature at the edge of the optimum selectivity. Without internalheat exchange to remain within the optimum selectivity, the methaneconversion is limited to about 10%, while with 31% internal heatexchange the methane conversion can be advantageously at about 15%,which an increase of about 50%.

A heat exchanger can be integrated with a mixer and OCM reactor. FIGS.10A, 10B and 10C are various views of an OCM system 1000 that is anintegrated heat exchanger and gas injection system. FIG. 10A is anisometric view, FIG. 10B is a cross-sectional side view, and FIG. 10C isa top view of the system 1000. The system 1000 comprises a gas inlet1001 that is in fluid communication with a fluid flow path 1002. Thefluid flow path 1002 can include a chamber that is in fluidcommunication with the inlet 1001 and the ribs 1003. The system 1000includes a plurality of ribs 1003. Each of the ribs 1003 is in fluidcommunication with the fluid flow path 1002 through one or more openings(e.g., holes or slits) at the ends of the ribs 1003. The ribs 1003 caneach be hollow. In the illustrated example, spaces between the ribs 1003are filled with an OCM catalyst.

A fluid (e.g., air) is directed into the system 1000 through the gasinlet 1001 and is directed through the fluid flow path 1002 (see, e.g.,FIG. 10C). From the fluid flow path 1002, the fluid is directed to eachrib 1003. The fluid is then directed to an end 1005 (see, e.g., FIG.10B) of each of the ribs 1003, where it is ejected out of the ribs 1003via one or more openings (e.g., holes or slits) at the end of the ribs1003. At the end 1005, the fluid can mix with an additional fluid 1006that is directed from a top portion of the system 1000.

In some examples, the fluid directed from the gas inlet 1001 through thefluid flow path 1002 includes an oxidizing agent, such as oxygen (O₂).The fluid can be air. The additional fluid 1006 can be methane. Fluidmixing can take place at the end 1005.

The ends 1005 are situated towards the top of the air foils. With suchconfiguration, the fluid can be directed through the ribs 1003 along adirection that is substantially opposite to the direction of flow of theadditional fluid 1006. As an alternative, or in addition to, the ribs1003 can include openings situated along the sides or at the bottom ofthe ribs 1003 such that the fluid exits the ribs at the sides or at thebottom.

The ribs 1003 can have various shapes, such as airfoil shapes. The ribs1003 can be formed of a ceramic or composite material, such as, forexample, alumina, zirconia and/or silicon carbide. The ribs 1003 can beairfoils.

FIG. 11A shows an OCM reactor that is integrated with a heat exchanger1100. The heat exchanger 1100 comprises a plurality of flow reversalpipes (ten shown). An individual flow reversal pipe 1101 includes aninner tube 1102 circumscribed by an outer tube 1103. A bottom portion1104 of the outer tube 1103 is closed. The pipe 1101 includes a fluidflow path between the inner tube 1102 and the outer tube 1103. The fluidflow leads from an inlet 1105 to the bottom portion 1104 and upward toan outlet 1106.

The heat exchanger 1100 includes a space 1107 between the pipes 1101that is filled with an OCM catalyst (not shown). The space 1107 can beat least partially or complete filled with the OCM catalyst. Forexample, the space 1107 can be at least partially or completely filledwith catalyst particles in a fluidized bed. The fluid flow path can bein thermal communication with the OCM catalyst such that heat liberatedin an OCM reaction is directed to the fluid flow path and a fluid in thefluid flow path.

The inlet 1105 can be at or above the OCM catalyst, such as a catalystbed of the OCM catalyst. As an alternative, the inlet 1105 can beexternal to the OCM catalyst.

The outlet 1106 can be in the OCM catalyst or above the OCM catalyst. Insome situations, the outlet 1106 is within the OCM catalyst, such as apacked bed. In such a case, the fluid stream can exit the individualpipe 1101 in the OCM catalyst.

During use, a fluid stream (e.g., air or methane) is directed from theinlet 1105 through the fluid flow path between the inner 1102 tube andthe outer tube 1103 to the outlet 1106. During an OCM reaction, heat maybe generated, which can be directed to the fluid stream in the fluidflow path. The heat can be used to heat the fluid in the fluid stream.At the outlet 1106, the fluid can be brought in contact with anotherfluid (e.g., methane) in a fluid stream external to the individual pipe1101 and mixed to provide a mixed stream, which can be directed to theOCM catalyst in the space 1107 to provide C₂₊ compounds and heat.

The heat exchanger 1100 can include at least 1, 2, 3, 4, 5, 6, 7, 8, 9,10, 15, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, or 1000pipes 1101, and in various arrangements. In some examples, the pipes1101 are in a side by side arrangement, circumferential arrangement, ora combination of the two arrangements.

In some cases, by using an open tube inserted into a capped tube, fluidflow can be forced to reverse direction between the inlet 1105 and theoutlet 1106. By inserting the flow reversal tube 1101 in an OCM catalystcomprising a packed bed, a pressure differential can be created underflow conditions that can provide the pressure drop to drive the fluidfrom the inlet 1105 to the outlet 1106.

In some situations, when a large rise in temperature is obtained throughan OCM reaction, the temperature of the stream exiting the individualpipe 1101 can be significantly higher than the temperature of the streamentering the individual pipe 1101.

FIGS. 11B and 11C are schematic cross-sectional and side views,respectively, of an integrated OCM reactor and heating element. Theheating element includes an OCM catalyst 1111 that is in between aninner fluid flow path 1112 and an outer fluid flow path 1113. The arrowsindicate the direction of fluid flow. An OCM gas (e.g., methane andoxygen) can be directed along the inner fluid flow path 1112 to generateC₂₊ compounds in an OCM process with the aid of an OCM catalyst 1111. Aheating exchange fluid can be directed along the outer fluid flow path1113 in a parallel flow (as illustrated) or cross-flow configurationwith respect to fluid flow along the inner fluid flow path 1112. Heatgenerated during the OCM process can be transferred to the heat exchangefluid in the outer fluid flow path 1113. The heat exchange fluid caninclude one or more OCM gases (e.g., methane and O₂), products of theOCM reaction (e.g., C₂₊ compounds), or a fluid that is configured totransfer energy to or remove energy from the OCM catalyst 1111. The OCMcatalyst 1111 can be a standalone inner tube or a coating on a supportmaterial.

The surface of the OCM catalyst 1111 that is exposed to the inner fluidflow path 1112 can have a temperature that increases from an inlet (leftportion) to an outlet (right portion) of the reactor of FIGS. 11B and11C. The temperature of a heat exchange fluid flow through the outerfluid flow path 1113 can increase or decrease based on the direction offluid flow. If the heat exchange fluid is flowing in parallel fashionwith respect to fluid flow in the inner fluid flow path 1112, then thetemperature of the heat exchange fluid can increase from inlet (leftportion) to outlet (right portion).

Integrated heat exchangers of the disclosure enable the creation andmaintenance of a hot spot within an OCM catalyst, allowing an OCMreactor to be operated with a reduced temperature inlet compared tocases in which an integrated heat exchanger is not used. In someimplementations, the inlet gas is heated to the necessary temperature bya heat exchanger, which enables the OCM reaction in a fixed bed reactor.This temperature can be between 300° C.-550° C. This approach may besensitive to the oxygen concentration in the feed and requiresubstantially short residence times from the heater to the catalyst bedto prevent combustion, such as via auto-ignition. The heat exchangercapital cost may also be an issue. For example, the inlet temperaturecan be about 350° C. for a fluidized bed reactor (in some cases withrelatively high reverse flow direction heat transfer), which can enableincreased conversion in an adiabatic bed as well as minimizing the riskof premature ignition, especially when using pure O₂ as the oxidizingagent in the OCM reaction.

In some embodiments, a heating element is lined externally with an OCMcatalyst (e.g., coated or a sleeve is placed over heater surface). Theheating element can have a relatively low heat transfer efficiency so asto maintain a high skin (or boundary layer) temperature of the OCMcatalyst that externally coats the heating element. As the inlet gaspasses adjacent to the heating element, gas near the surface of thecatalyst can be heated to a temperature that is at or near the skintemperature, which can initiate the OCM reaction and release heat thatcan mix with the bulk gas, uniformly heating the process gas stream. Theskin temperature of the OCM-catalyst lined heating element can besufficiently high so as to help ensure that the OCM reaction is highlyselective (e.g., from about 750° C. to about 900° C.) for a desirableproduct (e.g., C₂₊ compounds). In some cases, as the OCM reactionproceeds on the heating element surfaces, it produces heat thatincreases the inlet gas temp as well as produces desirable OCM reactionproducts (e.g., C₂₊ compounds, water). This can be an approach to bothreduce inlet heat exchanger capital costs as well as enable much highersingle stage conversions, because the inlet O₂ (or other oxidizingagent) concentration can be sufficiently high to heat the inlet gas fromlow temperatures (e.g., 25° C.−300° C.) to the desired reactor inlettemperature (e.g., 400° C.−600° C.). For example, ˜10% conversion ofmethane at a C2 selectivity approaching 60% heats the inlet gas from200° C. to 500° C. An additional 10% conversion can be attained in thefixed bed portion of the reactor, for example, resulting in a muchhigher single stage conversion. Heat exchangers lined with OCM catalystsof the present disclosure can take advantage of the substantially rapidOCM reaction kinetics at temperatures in excess of 750° C., which mayonly require a limited number of catalyst coated heating elements toheat the inlet gas, while still maintaining a substantially shortresidence times to prevent combustion prior to the catalyst bed. Thelimited number of tubes and poor heat transfer to the gas stream maykeep the heating duty of the inlet gas heat exchanger low, and the exitgas from the reactor can potentially be used as the heating medium. Insuch a case, at least an additional heater may be required to initiatethe reaction.

Integrated heat exchangers of the present disclosure can be used totransfer heat to a gas stream undergoing a homogeneous endothermicreaction, such as alkane cracking into alkenes. For example, an OCMreactor may include a cracking unit downstream of a catalyst unitcomprising an OCM catalyst. The cracking unit can be heated using heatgenerated in the catalyst unit in an OCM reaction.

Reactors of the present disclosure can be operated or designed tooperate with reduced linear velocity. Reduced linear velocity operationcan promote feed pre-heating. Reduced linear velocity operation canreduce axial convective heat transfer. Reduced linear velocity operationcan move the peak bed temperature location toward the front end of thebed. Reaction heat can be used for stream preheating. Reduced linearvelocity operation can result in reduced oxygen consumption in lowselectivity regions. Reduced linear velocity operation can increasereaction selectivity across the reactor. A reactor can operate withreduced linear velocity in part of or in the entire reactor. Forexample, a reactor can comprise a low linear velocity region followed bya high linear velocity region. Linear velocity can be controlled betweenreactor regions by changing the reactor diameter or width. A reactor cancomprise an annular reactor, wherein a feed stream enters the centralregion and flows from the central region to the outer region.

The linear velocity can be any suitably low value, such as about 3meters per second (m/s), about 2.5 (m/s), about 2 (m/s), about 1.5(m/s), about 1 (m/s), about 0.5 (m/s), about 0.4 (m/s), about 0.3 (m/s),about 0.2 (m/s), about 0.1 (m/s), or about 0.05 (m/s). In some cases,the linear velocity is equal to or less than about 3 meters per second(m/s), equal to or less than about 2.5 (m/s), equal to or less thanabout 2 (m/s), equal to or less than about 1.5 (m/s), equal to or lessthan about 1 (m/s), equal to or less than about 0.5 (m/s), equal to orless than about 0.4 (m/s), equal to or less than about 0.3 (m/s), equalto or less than about 0.2 (m/s), equal to or less than about 0.1 (m/s),or equal to or less than about 0.05 (m/s).

The present disclosure provides for tubular reactor systems. A tubularreactor can comprise a single stage. A tubular reactor can employ a heatremoval medium, such as molten salt. A heat removal medium can be usedfor heat removal from a reactor bed. A heat removal medium can be usedfor preheating feed streams. Tubular reactor systems can be used forreactions including but not limited to oxidative coupling of methane(OCM) and oxidative dehydrogenation of ethane (ODH). Temperature controlin a tubular reactor bed can be controlled by designing different bedproperties in segments. Such bed segmentation to the temperature profilecan be achieved by controlling the linear velocity of the reaction gas,for example by varying the tube diameter or by including non-reactivesleeves or inserts. Bed segmentation to control the temperature profilecan be achieved by controlling the thermal conductivity of the bed, forexample by controlling the catalyst form (e.g., shape, size, extrudates,rings, monoliths, foams) or by choice of catalyst support (e.g.,alumina, SiC, silica, magnesia). Bed segmentation to control thetemperature profile can be achieved by changing the thermal conductivityof the tube wall liner. Bed segmentation to control the temperatureprofile can be achieved by using multiple heat removal medium sectionswith varying levels of turbulence or temperatures.

The present disclosure provides for heat integration by flow reversal.Flow reversal can be alternating and sequential, including periodic flowreversal and non-periodic flow reversal. Flow reversal can occur with aperiod of about 1 nanosecond (ns), 10 ns, 100 ns, 1 millisecond (ms), 10ms, 100 ms, 1 second, 10 seconds, 20 seconds, 30 seconds, 40 seconds, 50seconds, 1 minute, 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50minutes, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8hours, 9 hours, 10 hours, 11 hours, 12 hours, or 24 hours. High reactiontemperature can result in more efficient recovery of heat fromexothermic reactions. A reactor system can be operated with periodicallyoperated flow reversal to achieve heat integration. A reactor system cansimulate a moving bed reactor to achieve heat integration. A fixed bedsystem can be employed with a moving high temperature front formed fromexothermic reaction. Travelling temperature fronts in reversed flow andsimulated moving bed reactors can give rise to unsteady state reactorsystems, with product gas composition changing over time.

Flow reversal reactors can be useful in managing the heat of reaction ofhighly exothermic reactions. They can enable heat integration where thecatalyst bed serves as the gas pre-heater and as the material carryingout the catalytic conversion and generating heat in the system. OCM is avery exothermic reaction and management of the heat of reaction can be alimiting factor in the operation of fix bed adiabatic reactors understeady state conditions.

Using periodic change of flow direction across the catalyst bed canpermit the operation of the catalyst under unsteady conditions. Forexample, the inlet gas feed temperature can drop below the extinctiontemperature of the catalyst bed under the pressure. The ability of usingpart of the bed as a heat exchanger opens the operating window of thereactor system.

FIG. 33 shows an example of a reactor system for flow reversal for OCMthat includes a reactor 3300 and a heat exchanger 3305 (e.g., steamgenerator). FIG. 33 shows a white space representing a volume betweenthe reactor and heat exchanger, i.e., the reactor and heat exchangerbeing separate vessels, however the reactor and heat exchanger can beregions within a single vessel. Reactants flow into 3310 the system andare converted to products over a catalyst bed 3315, which products flowout of the system 3320.

During normal operation, the valve switching the location of the feedinjection 3325 in the catalyst bed is actuated at regular intervals.This interval can depend on the exothermicity of the reaction, the heatcapacity of the catalyst bed and how far from the extinction temperaturethe feed conditions are. The period between flow reversals can be about5 seconds (s), about 10 s, about 15 s, about 20 s, about 30 s, about 40s, about 50 s, about 1 minute (min), about 2 min, about 3 min, about 5min, about 10 min, about 20 min, about 30 min, about 40 min, about 50min, about 60 min, about 90 min, about 120 min, or about 180 min. Insome cases, the direction of flow is reversed after a period of timebetween about 20 seconds and about 20 minutes. The second valveselecting the exhaust flow path 3330 in the reactor may be activatedsimultaneously or with some delay.

As shown in FIG. 33, depending on the position of the injection valve3325, the fluid (reactants and products) flows through the system in oneof two directions. The fluid is shown as gray shading and the flowdirection shown by dark black arrows. The valve can also be leaky suchthat at least some gas flows in both directions. The reactants can beinjected into the system through a first path 3335 or a second path3340. The reactant injection paths can be surrounded by the catalyst bed3315. In some cases, the injection paths are the mixers describedherein. The heat produced in the OCM reaction can convert water 3345 tosteam 3350.

Injecting the reactants within the catalyst bed can minimize unconvertedoxygen bypass when changing the flow direction, as the feed is alwaysflowing across active catalyst bed. This can be important if very rapidswitching is required (e.g., to prevent the hot spot in the reactor fromexiting the mid-section). The splitting of the bed and the in-bedinjection points also allow for imperfect seals in the three way valveused, as all gas going across this system can be processed and free fromoxygen. This enables the use of rugged design valves and or extendednumber of cycle operating life.

In some cases, the product gas on the way to the product flow directionselector valve 3330 is cooled to avoid damaging the valve. A steamgenerating heat exchanger can be used minimizing the number of pieces ofequipment 3305.

FIG. 34 shows the temperature profile through the catalyst bed (e.g.,when the inlet gas temperature is too low to maintain a stabletemperature profile through the reactor bed). The figures shows thesystem with fluid flowing through the system in a first direction 3400and in a second direction 3405. The expected temperature profile isplotted to the right of each flow schematic with the temperatureincreasing from left to right 3410 as a function of the position in thecatalyst bed from top to bottom 3415 (mirroring the schematic to theleft). The cold front shifts towards the back of the bed in the flowdirection. The bypass section of the bed slowly loses heat because noreaction is taking place there.

As the hottest spot in the bed is expected to be near the exit, when theflow direction is switched the hot spot will start migrating toward theother end of the reactor. By regularly reversing flow, the system can bemaintain in a stable thermal oscillating mode. One benefit of using sucha device and method can be an improved product yield compared to steadystate operation. Another benefit can be access of operating pressuresnot attainable in steady fix bed operation (e.g., due to un-stability ofthe feed at elevated temperature and pressure). Lowering the inlet feedtemperature can also improve the catalyst operating live. Furthermore,if the catalyst is susceptible to coking, changing the feed injectionpoint can periodically de-coke the back of the catalyst bed.

A reactor system can comprise manifolds for a packed bed reactor withreverse flow. FIG. 12 shows an inlet manifold 1201 and an outletmanifold 1202. Each manifold can comprise a plurality of parallel tubes.Manifolds can be assembled into a sandwich configuration comprising acatalytic packed bed 1203. Manifolds, such as inlet and outletmanifolds, can be assembled with their tubes interdigitated with eachother. Feed gas stream 1204 can be fed into the inlet manifold. Productgas stream 1205 can exit from the outlet manifold. A counter flow 1206can be produced within the catalyst bed due to the manifoldconfiguration. Manifolds and tubes can be made of materials includingbut not limited to one or more metals, dense ceramics (e.g., alumina),silicon carbide, and vitreous materials (e.g., quartz). A manifold cancomprise at least about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30,35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 200, 300, 400,500, 600, 700, 800, 900, 1000, or more tubes. The inlet manifold cancomprise radiators mounted on the inlet side to promote heat exchangebetween the reactor product stream and the feed stream. Manifold reactorconfigurations can enable increased heat exchange between reactor inletand reactor outlet streams. Manifold reactor configurations can enableoperation at lower inlet temperatures. Manifold reactor configurationscan allow operation to take advantage of the difference between lightoff temperature and extinction temperature in highly exothermiccatalytic processes. This approach can reduce the number of heatexchanger stages needed to achieve a particular overall conversion orselectivity. This approach can improve catalyst life.

Methods for Improving Olefin Yield

An aspect of the present disclosure provides OCM systems and methods forincrease the concentration of alkenes (or olefins) in C₂₊ compoundsoutputted from an OCM reactor. This can advantageously provide C₂₊product stream that may be better suited for downstream uses, such asthe commercial production of polymeric materials, as well as greatercarbon efficiency of the overall process. In some embodiments, an OCMsystem provides improved alkene yield by alkane cracking in a catalystunit or cracking unit. Such in situ cracking of alkanes can provide aproduct stream with hydrocarbon distributions tailored for various enduses.

FIG. 13 shows an OCM system 1300 comprising an OCM reactor 1301, acracking unit 1302 downstream of the OCM reactor 1301, and at least oneseparation unit 1303 downstream of the cracking unit 1302. The OCMreactor 1301 and cracking unit 1302 can be separate units or integratedas a single unit, as illustrated by the dashed box. The arrows indicatethe direction of fluid flow from one unit to another. During use, afirst fluid stream (“stream”) 1304 comprising methane (CH₄) and a secondfluid stream 1305 comprising an oxidizing agent (e.g., O₂) are directedinto the OCM reactor 1301, where they react in the presence of acatalyst provided within reactor 1302 to form C₂₊ compounds, which areincluded in a third stream 1306. The third stream 1306 can include otherspecies, such as non-C₂₊ impurities like Ar, H₂, CO, CO₂, H₂O, N₂, NO₂and CH₄. The third stream 1306 comprises OCM products, which can includeC₂₊ compounds and non-C₂₊ impurities.

Next, the third stream 1306 is directed to the cracking unit 1302. Inthe cracking unit 1302, alkanes in the C₂₊ compounds can react to formC₂₊ compounds with unsaturated moieties, which are outputted from thecracking unit 1302 in a forth stream 1307, such as carbon-carbon doublebonds (e.g., ethylene and propylene). The fourth stream 1307 can then bedirected to other unit operations for processing gases in the fourthstream 1307, such as the separation unit 1303 used for separation of atleast some, all, or substantially all of the C₂₊ compounds from othercomponents in the fourth stream 1307 to yield a fifth stream 1308 and asixth stream 1309. The streams 1308 and 1309 can each be directed to oneor more storage units. The fifth stream 1308 can be directed to C₂₊storage or a non-OCM process.

Methane in the first fluid stream 1304 can be provided from any of avariety of methane sources, including, e.g., a natural gas source (e.g.,natural gas reservoir) or other petrochemical source, or in some casesrecycled from product streams. Methane in the first fluid stream may beprovided from an upstream non-OCM process.

The fifth stream 1308 can include C₂₊ (e.g., olefins) compounds at aconcentration (e.g., mole % or volume %) that is at least about 10%,20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, or 99%, and the sixthstream 1309 can include C₂₊ compounds at a concentration that is lessthan about 99%, 95%, 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, or 10%. Thesixth stream 1309 can include methane at a concentration of at leastabout 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, or 99%. Theconcentration of C₂₊ compounds in the fifth stream 1308 can be higherthan the concentration of C₂₊ compounds in the sixth stream 1309. Thesixth stream 1309 can include other species, such as Ar, H₂, CO, CO₂,H₂O, N₂, NO₂ and CH₄. At least some, all or substantially all of CH₄and/or O₂ in the sixth stream 1309 may optionally be recycled to the OCMreactor 1301 and/or the cracking unit 1302 in a seventh stream 1310.

The at least one separation unit 1303 can include a plurality ofseparation units, such as at least 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30,40, or 50 separation units, at least some of which can be in seriesand/or parallel. In some examples, the at least one separation unit 1303is a full separation train, in some cases including one or moredistillation columns, scrubbers, etc. The at least one separation unit1303 can include an olefin/alkane splitter and/or CO₂ separation unit.The seventh stream 1310 can include C1 (methane) recycle to the OCMreactor 1301 and/or the cracking unit 1302.

In some examples, at least about 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%,50%, 60%, 70%, 80%, or 90% of the non-C₂₊ components (e.g., CH₄ and/orN₂) of the fourth stream 1307 can be separated by the separation unit1303 and directed along the sixth stream 1309. This can provide a fifthstream 1308 that has a higher concentration of C₂₊ compounds, includingolefins and higher molecular weight alkanes.

The system 1300 can include any number of OCM reactors 1301 and crackingunits 1302. The system 1300 can include at least 1, 2, 3, 4, 5, 6, 7, 8,9, or 10 OCM reactors 1301. The OCM reactors 1301 can be the same,similar or dissimilar reactors or reactor types arranged in series orparallel processing trains. The OCM reactors 1301 can be in seriesand/or in parallel. The system 1300 can include at least 1, 2, 3, 4, 5,6, 7, 8, 9, or 10 cracking units 1302. The cracking units 1302 can bethe same, similar or dissimilar reactors or reactor types arranged inseries or parallel processing trains. The cracking units 1302 can be inseries and/or in parallel. Alternatively, the reactor 1301 can be usedas a cracking unit by periodically changing the feed of the reactorbetween OCM feed to a C₂₊ alkane rich feed. In such a case, the heatcapacity of a catalyst bed in the reactor 1301 can be used for alkanecracking.

The system 1300 can include at least 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10separation units. In the illustrated example, the system 1300 includesone separation unit 1303. The separation unit 1303 can be, for example,a distillation column, scrubber, or absorber. If the system 1300includes multiple separation units 1303, the separation units 1303 canbe in series and/or in parallel.

Although described for illustration of certain aspects as gas streamspassing into, through and out of the reactor systems in FIG. 13, it willbe appreciated that the streams 1304, 1305, 1306, 1307, 1308, 1309 and1310 can be gaseous streams, liquid streams, or a combination of gaseousand liquid streams. In some examples, the streams 1304 and 1305 aregaseous streams, and the stream 1308 and 1309 are liquid streams.

In some examples, the separation unit 1303 can include more than twoproduct streams. For example, olefins can be directed out of theseparation unit 1303 along an olefin stream and ethane and propane canbe directed out of the separation unit 1303 along another stream. Thesixth stream 1309 may be dedicated to methane.

The OCM reactor 1301 can include any vessel, device, system or structurecapable of converting at least a portion of the third stream 1306 intoone or more C₂₊ compounds using an OCM process. The OCM reactor 1301 caninclude an adiabatic fixed bed reactor where the combined methane/oxygengas mixture is passed through a structured bed that can include anactive temperature control component (e.g., molten salt cooling systemor the like), an isothermal tubular fixed bed reactor where the combinedmethane/oxygen gas mixture is passed through a structured bed, anadiabatic radial fixed bed reactor where the combined methane/oxygen gasmixture is passed through a structured bed, a fluidized bed reactorwhere the combined methane/oxygen mixture is used to fluidize a solidcatalyst bed, a honeycomb, and/or a membrane type reactor where thecombined methane/oxygen mixture passes through an inorganic catalyticmembrane. In some cases, a radial fixed bed reactor may be used as theheat loss in the collection volume is minimized when inward flow isused. The cracker section outer wall may be the diffuser of the OCMreactor.

The cracking unit 1302 can be a chamber or a plurality of chambers, suchas a plurality of vessels or pipes. The cracking unit 1302 can includeinlets for accepting compounds at various locations along the crackingunit 1302. The cracking unit 1302 can have a temperature profile acrossthe cracking unit 1302 and along a direction of fluid flow leading froman inlet of the cracking unit 1302 to an outlet of the cracking unit1302. In some examples, an upstream portion of the cracking unit 1302 ishotter than a downstream portion of the cracking unit 1302.

The system 1300 can include a mixer upstream of the OCM reactor 1301.The mixer can be employed for use in pre-conditioning OCM reactants,which can prevent the auto-ignition of the reactant gases prior to theOCM process in the OCM reactor 1301.

The cracking unit 1302 may be integrated into one or more unitoperations of an overall OCM process system. For instance, although theOCM reactor 1301 and cracking unit 1302 are illustrated in FIG. 13 asseparate unit operations, the cracking unit 1302 can be part of the OCMreactor 1301. In some cases, the cracking unit 1302 is positionedimmediately adjacent to the catalyst bed within the reactor 1301, sothat that the C₂₊ compounds may be more rapidly introduced to thecracking unit 1302 (see, e.g., FIGS. 15A and 15B). When integrating theOCM reactor 1301 with the cracking unit 1302, improved heat integrationcan be obtained by using a radial fixed bed reactor as illustrated inFIG. 15B.

FIG. 14 shows a system 1400 comprising an OCM reactor 1401 with acatalyst unit 1402 and a cracking unit 1403 downstream of the catalystunit 1402. The catalyst unit 1402 can be a packed bed, for example. Thesystem 1400 further comprises an oxidizing agent source 1404 directedinto the reactor 1401. The oxidizing agent source 1404 can provide anoxidizing agent, such as O₂, which can be provided by way of air.Various hydrocarbon sources are directed into reactor 1401. In theillustrated example, a methane source 1405 and a hydrocarbon recycle1406 are combined with the oxidizing agent source 1404. The methanesource 1404 supplies methane and the hydrocarbon source 1405 supplieshydrocarbons, such as a portion of the C₂₊ compounds generated by theOCM reactor 1401.

The cracking unit 1403 can include a heterogeneous catalyst that may besuitable for cracking alkanes to other types of hydrocarbons, such asalkenes. As an alternative, the cracking unit 1403 does not include aheterogeneous catalyst, but is configured to perform adiabaticallyusing, for example, heat provided by steam that is generated in the OCMreaction in the catalyst unit 1402.

A natural gas plant 1407 supplies natural gas from a natural gas source1408 to a natural gas pipeline 1409, which subsequently supplies naturalgas to a separations unit 1410. The separations unit 1410 separatesmethane from other hydrocarbons (e.g., ethane, propane, butane, etc.)and supplies methane to the reactor 1401 in the methane source 1405. Theother hydrocarbons, such as higher hydrocarbons (e.g., ethane), aresupplied along stream 1411 to the reactor 1401. Other alkanes from thenatural gas plant 1407 can be directed to the reactor 1401 along stream1412.

As shown, the streams 1411 and 1412 are injected into the cracking unit1403 at different points. As an alternative, or in addition to, thestreams 1411 and 1412 can be injected into the reactor 1401 at the samepoint. In some situations, at least some of the streams 1411 and 1412can be injected into the catalyst unit 1402.

In the OCM reactor 1401, methane and an oxidizing agent react to yieldOCM products comprising C2+ compounds, which are directed along an OCMproduct stream 1413 to separations unit 1414. The separations unit 1414separates at least a portion of the C₂₊ compounds from lower molecularweight hydrocarbons (e.g., methane) and/or non-C₂₊ impurities in the OCMproduct stream 1413. A C₂₊ compound product stream 1415 is directed fromthe separations unit 1414 for downstream use, such as non-OCM processesor storage. Lower molecular weight hydrocarbons, such as methane, aredirected along stream 1416 to a storage unit 1417, which cansubsequently direct the lower molecular weight hydrocarbons to thereactor 1401 along the hydrocarbon recycle stream 1406. At least aportion of the lower molecular weight hydrocarbons can be purged fromthe storage unit 1417 via a purge 1418

In some instances, in the OCM reactor 1401 at least a portion of themethane can react with an oxidizing agent (e.g., oxygen) in the presenceof the one or more catalysts to provide an OCM product stream comprisingone or more C₂₊ compounds, including at least ethane and ethylene. Thehydrogen liberated during the conversion of methane to the one or moreC₂₊ compounds can combine with the oxygen to form water. Any oxygenpresent also can combine with at least a portion of the carbon presentin the methane to form carbon dioxide. The overall conversion of methaneand oxygen to one or more C₂₊ compounds can be dependent upon at leastcatalyst composition, reactant concentration, and reaction temperatureand pressure within the OCM reactor 1401, the thermal profile throughthe one or more catalysts in the OCM reactor 1401, the maximumtemperature within the one or more catalysts, the maximum temperaturerise within the one or more catalysts, or combinations thereof.

In addition to the one or more C₂₊ compounds, the OCM product streamgenerated in the OCM reactor 1401 may also contain residual un-reactedmethane, residual un-reacted oxygen, water, and carbon dioxide. Ethanecan also be present in OCM product stream. The ethane concentrationwithin the OCM product stream can be at least about 0.25 mol %; at leastabout 0.5 mol %; at least about 0.75 mol %; at least about 1 mol %; atleast about 1.5 mol %; at least about 2 mol %; at least about 2.5 mol %;at least about 3 mol %; at least about 3.5 mol %; at least about 4 mol%; at least about 4.5 mol %; or at least about 5 mol %. Ethylene willalso be present in the OCM product stream. The ethylene concentrationwithin the OCM product stream can be at least about 0.25 mol %; at leastabout 0.5 mol %; at least about 0.75 mol %; at least about 1 mol %; atleast about 1.5 mol %; at least about 2 mol %; at least about 2.5 mol %;at least about 3 mol %; at least about 3.5 mol %; at least about 4 mol%; at least about 4.5 mol %; or at least about 5 mol %.

The conversion of methane to higher molecular weight hydrocarbons, suchas ethane and ethylene, can be dependent upon the residence time ofreactants such as methane, ethane, and higher hydrocarbons in the OCMreactor 1401. In particular, the ratio of ethane to ethylene can bedependent upon the residence time of reactants, such as methane, ethane,and higher hydrocarbons in the OCM reactor 1401 at temperatures inexcess of about 800° C. Experience has shown that the formation ofethylene within the OCM reactor 1401 may occur as a secondary reactionthat may rely upon a steam or thermal cracking process rather than anoxidative process. Thus, the conversion of ethane to ethylene may occurat the elevated temperatures of the OCM reaction, either in portions ofthe OCM reactor 1401 or immediately following the OCM reactor 1401 wherethe oxidant concentration is reduced.

In some cases, at least a portion of the ethane present in the OCMproduct stream can be separated and recycled back into the OCM reactor1401 in order to convert that ethane to ethylene. In some embodiments,at least a portion of the ethane is separated from the OCM productstream, e.g., by passing the OCM product stream or a portion thereofthrough a downstream or post-production cryogenic separation process.See, for example, U.S. patent application Ser. No. 13/739,954, filedJan. 11, 2013, which is entirely incorporated herein by reference forall purposes. In some instances, at least a portion of the separatedethane may be re-injected directly into the OCM reactor 1401 at one ormore points along the OCM reactor 1401, including within the catalystunit, the cracking unit 1403, or both. The location of injection orre-injection can be selected to effect a given product distribution outof the OCM reactor 1401, such as a higher proportion of alkenes ascompared to alkanes.

In some cases, ethane or other alkanes are injected into the OCM productstream at a location in, at, or in proximity to the OCM reactor 1401.This can advantageously enable the use of process conditions to crackalkanes to alkenes, such as ethane to ethylene. In some examples,alkanes are cracked with the aid of steam. While this cracking of analkane to alkene (e.g., ethane to ethylene) can also be achieved byinjecting the alkane at an earlier stage, the prolonged exposure to theelevated temperature may detrimentally result in greater combustion ofthe alkane to alkene through the OCM reactor 1401. The alkane can beprovided as recycle from the OCM product stream comprising C₂₊ productsproduced by the OCM reactor 1401. As an alternative, or in addition to,the alkane can be provided from an exogenous source, such as, forexample, an ethane output from a natural gas liquids (NGL) processingfacility, or the like.

One or more higher hydrocarbons can be combined with the OCM productstream prior to cooling the OCM product stream. In some embodiments, oneor more higher hydrocarbons can be introduced to a catalyst unit 1402 orthe cracking unit 1403 in the OCM reactor 1401. To reduce the likelihoodof forming undesirable byproducts, the oxygen concentration in the OCMproduct stream at the point of combination with the one or more higherhydrocarbons can be less than about 5 mole %, less than about 2 mol %,less than about 1 mol %, less than 0.5 mol %, or less than 0.1 mol %. Toimprove the yield of desirable higher hydrocarbon products (e.g.,alkenes), the temperature of the OCM product stream at the point ofcombination with the one or more higher hydrocarbons can be greater thanabout 600° C.; greater than about 650° C.; greater than about 700° C.,greater than about 750° C.; greater than about 800° C.; greater thanabout 850° C.; greater than about 900° C., or greater than about 920° C.In some embodiments, the temperature of the higher hydrocarbons may beincreased prior to combination with the OCM product stream orintroduction to the OCM reactor 1401 to minimize the cooling effect ofthe higher hydrocarbons on the OCM gas. In some embodiments, prior tocombining with the OCM product stream or being introduced to the OCMreactor 1401, the temperature of the higher hydrocarbons can beincreased to a temperature less than about 750° C.; less than about 700°C.; less than about 650° C.; or less than about 600° C.

In some cases, significant cracking of an alkane to an alkene (e.g.,ethane to ethylene) can occur when the alkane is introduced within thecatalyst bed of the OCM reactor 1401. At the same time the amount ofselectivity of the OCM reaction can be only slightly affected by theaddition of up to 20 mol % alkane (e.g., ethane, or propane, or butane)into the OCM product stream generated in the catalyst unit 1402. See,e.g., U.S. patent application Ser. No. 13/900,898, filed May 23, 2013,which is entirely incorporated herein by reference for all purposes.

Ethane or one or more higher hydrocarbons (e.g., alkanes) may beintroduced at any point in the OCM reactor 1401, including at one ormore points in the streams 1405 or 1406, the catalyst unit 1402, and/orthe cracking unit 1403. In some embodiments, ethane may bepreferentially introduced at locations in the OCM reactor 1401 where theconcentration of the oxidizing agent is reduced to lessen the formationof undesirable reaction byproducts, such as coke and similar long chaincombustion byproducts. The ethane or one or more higher hydrocarbons maybe introduced to the catalyst unit 1402 using one or more distributorsfabricated from one or more non-reactive materials, for instance aceramic oxide coated high temperature compatible metal or metal alloysuch as Inconel, Hastelloy, and Alloy N155 and the like. In at leastsome implementations the one or more distributors may include a thermalcontrol system to limit the temperature of the distributor and therebylessen the likelihood of occurrence of premature cracking of the ethaneor the one or more higher hydrocarbons prior to the introduction of theethane or one or more higher hydrocarbons to the OCM reactor 1401.

In at least some embodiments, one or more higher hydrocarbons, forinstance recovered ethane or C₁-C₄ light ends captured in an ethylene toliquids separations process subsequent to the OCM reactor 1401, may beintroduced to the OCM reactor 1401, at a point before the OCM reactor1401 (e.g., by mixing with the methane source 1405), or after the OCMreactor 1401 (e.g., by mixing with the OCM gas). In some embodiments, atleast a portion of the one or more higher hydrocarbons may be introduceddirectly within the catalyst unit 1402. Alternatively, or in additionto, at least a portion of the one or more higher hydrocarbons may beintroduced to the OCM gas prior to cooling the OCM gas in a thermaltransfer device fluidly coupled to the OCM reactor 1401. For instance,at least a portion of the one or more higher hydrocarbons can beintroduced directly to the cracking unit 1403.

FIG. 15A shows an OCM reactor 1501 comprising a catalyst unit 1502 and acracking unit 1503. The catalyst unit 1502 can be, for example, a packedbed reactor comprising a heterogeneous catalyst. The catalyst unit 1502can be configured to perform an OCM process using natural gas and O₂inputted into the reactor 1501. The cracking unit 1503 is configured toperform crack alkanes (e.g., ethane) to other types of hydrocarbons,such as alkenes (e.g., ethylene). The cracking unit 1503 can beconfigured to operate adiabatically using heat liberated in the catalystunit 1502 in the OCM process, which heat can be conveyed by way of steamgenerated in the OCM process, for example.

Various reactor types may be employed for use as the OCM reactor 1501.In some examples, the OCM reactor 1501 is a fixed bed reactor, fluidizedbed reactor, tubular isothermal reactor or a combination thereof. Afixed bed reactor can be an adiabatic fixed bed reactor. In someexamples the OCM reactor 1501 comprises multiple reactors in series. Insome cases, the OCM reactor 1501 can be operated at elevated pressures,such as between 1.5-50 bars (absolute), or 2-20 bars (absolute). In somesituations, the catalyst unit 1502 can include catalyst particles in theform of nanostructures (e.g., nanowires).

In some cases, steam formed in the OCM process in the catalyst unit 1502can aid in lowering the partial pressure of alkanes in an OCM productstream, thereby preventing and/or reducing the potential for carboncoking or deposition in the cracking unit. In some situations, in orderto minimize OCM product destruction, such as via combustion or carboncoking/deposition, higher chain or molecular weight hydrocarbons can beinjected in an oxygen-depleted region of the OCM reactor 1501, such asin the cracking unit 1503. Steam generated in the catalyst unit 1502 canbe directed to the cracking unit 1503 at various points along thecracking unit 1503.

During use, the catalyst unit 1502 can have an average temperaturebetween about 450° C. and 1200° C., or 500° C. and 1000° C. The catalystunit 1502 can have an inlet with an inlet temperature and an outlet withan outlet temperature. During use, the inlet temperature can be lessthan the outlet temperature. A temperature gradient may exist across thecatalyst unit 1502 along a direction of fluid flow (i.e., from inlet tooutlet). In an example, during use an inlet of the catalyst unit 1502 isat a temperature of about 520° C. and an outlet of the catalyst unit1502 is at a temperature of about 900° C. In some examples, the inletcan have a temperature that is less than or equal to about 750° C., 730°C., 710° C., 700° C., 690° C., 670° C., 650° C., 630° C., 610° C., 600°C., 590° C., 570° C., 550° C., 520° C., 510° C., 490° C., 470° C., or450° C. The outlet may have a temperature that is less than or equal toabout 850° C., 860° C., 870° C., 880° C., 890° C., 900° C., 910° C.,920° C., 930° C., 940° C. or 950° C. The outlet temperature can begreater than the inlet temperature. The catalyst unit 1502 can be partof a multistage unit comprising the cracking unit 1503 as the laststage. Cooling of the OCM products may occur in the cracking unit 1503.

The cracking unit 1503 can be used to form a given type or distributionof hydrocarbons. In some embodiments, the cracking unit 1503 can be usedto generate an OCM product stream with a higher proportion of alkeneproducts as compared to alkane products, such as a greater proportion ofethylene as compared to ethane. Various properties of the OCM reactor1501, including operating conditions, can be selected to increase alkeneto alkane ratios in OCM product streams. The operating conditions caninclude, without limitation, product recycle (e.g., CH₄ recycle), thecatalyst used in the catalyst unit 1502, the size and shape of the OCMreactor 1501, the size and shape of the cracking unit 1503, OCM reactortemperature, the temperature or temperature distribution in the crackingunit 1503, and stream (e.g., hydrocarbon-containing stream) residencetime in the cracking unit 1503. In some embodiments, the streamresidence time (e.g., post-bed residence time) and cracking unittemperature are controlled to yield a given product distribution. One ormore operating conditions of the OCM reactor 1501, including thecracking unit 1503, can be selected such that a molar ratio of C₂₊alkene to C₂₊ alkane in a product stream out of the OCM reactor 1501 isgreater than or equal to about 0.1, 0.2, 0.3, 0.5, 0.6, 0.8, 1, 2, 3, 4,5, 6, 7, 8, 9, 10, 12, 14, 16, 18, 20, 30, 40, 50, 60, 70, 80, 90, 100,or greater. In some cases, the molar ratio of C₂₊ alkene to C₂₊ alkaneis limited by thermodynamic equilibrium, which can be about 6 when wateris present at 6% and H₂ is present at 2%.

Stream residence time in the cracking unit 1503 can be controlled byregulating the flow rate of oxygen (or other oxidizing agent) and/ormethane into the OCM reactor 1501 or the flow rate of OCM products outof the OCM reactor 1501. The flow rate can be regulated with the aid ofvalves and fluid flow system (e.g., pumps) that can be under the controlof a computer system programmed to regulate process parameters, asdescribed elsewhere herein.

In the cracking unit 1503, the high heat capacity of OCM productsgenerated in the catalyst unit 1502 can be used to drive the endothermiccracking of alkanes to alkenes or other types of hydrocarbons (e.g.,alkynes). Moreover, the thermal heat capacity of the OCM effluent may besubstantially high such that it can be used to further convertadditional alkanes (e.g., ethane and propane) to alkenes-more than whatis present in OCM effluent—to alkenes (e.g., ethylene and propylene) inthe cracking unit 1503 of the OCM reactor 1501.

In some examples, ethylene/ethane ratios can increase with increasingOCM reactor 1501 size. For example, the ethylene to ethane ratios in theOCM product stream can increase in going from 4 millimeters (mm) to 8 mmto 2 inch OCM reactors. In some situations, radial reactors may be usedto shield the cracking section from cooler reactor walls. Generally, theincreasing C₂₊ alkene to alkane ratio may be a reflection of theincreasing adiabaticity the cracking reaction, which may be the resultof increasing diameter or cross-sectional size of the reactor 1501.Higher adiabaticity can lead to higher reactor temperatures, which canassist in thermal cracking of paraffins (ethane, propane, etc.) in thecracking unit 1503, leading to increasing olefins output from the OCMreactor 1501.

The cracking unit 1503 can have various sizes and configurations. Insome cases, the cracking unit 1503 includes one or more tubes eachcomprising a fluid flow path leading form an inlet to an outlet of atube. A residence time of a hydrocarbon stream directed through thecracking unit 1503 can be a function the size of the cracking unit 1503.In some examples, the cracking unit 1503 has a cross-section size (e.g.,diameter) of at least about 1 inch, 2 inches, 3 inches, 4 inches, 5inches, 6 inches, 12 inches, 16 inches, 24 inches, 36 inches, 48 inches,60 inches, 6 feet, 7 feet, 8 feet, 9 feet, 10 feet, 11 feet, 12 feet, 13feet, 14 feet, 15 feet, 20 feet, 30 feet or more. The residence time ofthe OCM product gas in the cracking unit 1503 can be less than or equalto about 2000 milliseconds (ms), 1000 ms, 500 ms, 400 ms, 300 ms, 200ms, 100 ms, 50 ms, or 10 ms

Olefins yield can be improved by addition of external alkanes (e.g.,ethane and/or propane) to the catalyst unit 1502, the cracking unit1503, or both. Natural gas can be the source of ethane, propane,butanes, and other hydrocarbons used to increase olefins yield. Processvariables such residence time (e.g., residence time in the cracking unit1503) and inlet temperature can be used to control OCM productdistribution. As an alternative, or in addition to, alkanes can beprovided to the cracking unit 1503 as recycle from the OCM productsgenerated in the OCM reactor.

In some embodiments, optimum performance may be achieved by using OCMproduct residence times in the cracking unit 1503 that are less thanabout 2000 milliseconds (ms), 1000 ms, 500 ms, 400 ms, 300 ms, 200 ms,100 ms, 50 ms, or 10 ms, at a cracking unit 1503 temperature from about800° C. and 950° C., or 810° C. to 900° C. In some cases, the crackingunit 1503 has an inlet temperature (at a location adjacent to thecatalyst unit 1502) that is from about 850° C. to 1000° C., or fromabout 880° C. to 950° C., and an outlet temperature that is from about750° C. to 850° C., or about 780° C. to 820° C.

In some example, ethane is injected into the cracking unit 1503 at atemperature that is less than or equal to about 850° C., 860° C., 870°C., 880° C., 890° C., 900° C., 910° C., 920° C., 930° C., 940° C. or950° C. In some cases, this temperature is an outlet temperature of thecatalyst unit 1502. Propane is injected into the cracking unit 1503 at atemperature that is less than the temperature at which ethane isintroduced into the cracking unit. In some cases, propane is introducedto the cracking unit 1503 at a temperature that is less than or equal toabout of 700° C., 710° C., 720° C., 730° C., 740° C., 750° C., 760° C.,770° C., 780° C., 790° C. or 800° C. Butane can be injected into thecracking unit 1503 at a temperature that is less than the temperature atwhich propane is injected into the cracking unit 1503. In some cases,butane is introduced to the cracking unit 1503 at a temperature that isless than or equal to about of 600° C., 610° C., 620° C., 630° C., 640°C., 650° C., 660° C., 670° C., 680° C., 690° C. or 700° C. Propane canbe injected into the cracking unit 1503 at a location that is downstreamfrom the location at which ethane is injected into the cracking unit1503. Butane (or other higher molecular weight alkanes) can be injectedinto the cracking unit 1503 at a location that is downstream from thelocation at which propane is injected into the cracking unit 1503.

In some examples, alkene yield from the OCM reactor 1501 is optimized byselecting an OCM product residence time from about 100 ms and 500 ms. Bycarefully controlling the residence times (e.g., less than 500 ms) andtemperature profile in the cracking unit 1503, the proportion ofundesirable C₂₊ products (e.g., ethane) as compared to desirable C₂₊products (e.g., ethylene) in the OCM product stream may be reduced. Insome cases, to minimize the OCM product destruction, higher molecularweight hydrocarbons may be injected in the oxygen-depleted region of theOCM reactor 1501, such as the cracking unit 1503. In some situations, anincrease in alkene yield can be advantageously realized with minimalincrease in capital expenditure, which can enable the formation ofdesirable alkene products in the OCM product stream with little or noincrease in operating cost.

Alkane cracking in the cracking unit 1503 can also lead to a higherconcentration of hydrogen in the OCM product stream out of the OCMreactor 1501. The effective carbon efficiency in an OCM process can besignificantly increased by methanation of CO and CO₂ with H_(z), e.g.,CO₂+2 H₂→CH₄+2 H₂O. Methane can be recycled back to OCM. In an example,any hydrogen formed in the OCM reactor via alkane cracking in thecracking unit 1503 may be converted to methane via reaction with CO orCO₂, and the methane can be separated in a separation unit downstream ofthe OCM reactor 1501 and recycled to the OCM reactor 1501 (e.g., viahydrocarbon recycle 1406 of FIG. 14). Such methanation can take place ina diluted stream with no pre-separation of the CO and H₂ from themethane. This can advantageously reduce the need to clean up the recyclestream in cases in which pure or substantially pure O₂ is used.

Process parameters may be controlled to effect a given productdistribution. Because of higher reactivity, hydrocarbon crackingseverity can increases with increasing carbon number of the hydrocarbon.For instance, the cracking severity of propane is higher than thecracking severity of ethane at a given inlet temperature of the crackingunit 1503. In some situations, the temperature of the cracking unit 1503can be lowered with increasing carbon number to increase the olefinyield and selectivity. The temperature can be regulated (i.e.,maintained, lowered or increased) with the aid of a computer system thatis programmed to regulate properties of the OCM reactor 1501.

Alkane cracking in the OCM reactor 1501 to form other hydrocarbons, suchas alkenes, may be sequential. In some cases, alkane cracking iscommenced with ethane followed by propane and other higher hydrocarbons.For example, with the cracking unit 1503 at 900° C., ethane is injectedinto the cracking unit 1503, which can decrease the temperature of thecracking unit 1503. Once the temperature of the cracking unit 1503 hasdecreased to below 800° C., for example, propane can be injected intothe cracking unit 1503. In some cases, once the temperature of thecracking unit 1503 has decreased to a temperature at or below 700° C.,butane can be injected into the cracking unit 1503. A mixed alkanestream can be injected at a point in the cracking unit 1503 at a streamtemperature that is less than or equal to about 900° C., 850° C., 800°C., 750° C., 700° C., 650° C. or 600° C.

As an alternative, or in addition to, alkanes can be injected into thecracking unit 1503 at locations that are selected to have a temperaturethat is suitable for a given alkane. For example, ethane cracking may beoptimum at 900° C. and propane cracking may be optimum at 850° C. Ethanecan be injected into the cracking unit 1503 at a location that is closerto the catalyst unit 1502 and propane can be injected into the crackingunit 1503 at a location that is further away from the catalyst unit1502, as shown in FIG. 15A.

The temperature at various locations across the OCM reactor 1501,including the cracking unit 1503 can be detected using temperaturesensors and relayed to a computer system. The computer system can thendetermine the appropriate hydrocarbon to inject into the cracking unit1503 at a measured temperature. For example, if the measured temperatureis 900° C., the computer system can direct the flow of ethane into thecracking unit 1503. In some cases, ethane is directed into the crackingunit 1503 from an external source, such as a natural gas source. Ethanecan be selected over other hydrocarbon in the natural gas source using aseparation unit (e.g., separation unit 1410 of FIG. 14).

The catalyst unit 1502, the cracking unit 1503, or both can beintegrated with a heat exchanger that is configured to remove heat from,or direct heat to, a respective unit. In an example, an integrated heatexchanger is configured to remove heat from the catalyst unit 1502during the OCM process and direct the removed heat to the cracking unit1503.

FIG. 15B shows the OCM reactor 1501 in a radial fixed bed configuration.At least a portion of the cracking unit 1503 is circumscribed by atleast a portion of the catalyst unit 1502. Ethane can be injected intothe cracking unit 1503 at a location upstream of the point at whichpropane is injected into the cracking unit 1503. In the illustratedexample, ethane is injected into the cracking unit 1503 at a temperatureof about 900° C., and propane is injected into the cracking unit 1503 ata temperature of about 850° C. The locations (and temperatures) at whichexternal alkanes are injected into the cracking unit 1503 can beselected to effect a given product distribution and conversion.

Thermodynamic and kinetic modeling studies of the adiabatic crackingpost OCM catalyst bed (see FIGS. 16 and 17) indicate that the alkeneyield may be increased using OCM reactors with cracking units, such aspost-bed reactor units. In some cases, the ethylene yield in an OCMreactor can be increased by at least a factor of two using OCM reactorswith post-reactor cracking units, as described above. For example, at apressure of about 8 bar (gauge), the percentage of ethylene exitingOCM-assisted cracking section can be as high as about 3.5%, 4.5%, 5.5%,6.5%, 7.5%, or more with an injection of about 4%, 5%, 6%, 7%, 8%, ormore ethane into the cracking unit 1503. FIG. 16 shows the mole fractionof ethylene as a function of the mole fraction of ethane at variousresidence times (50 ms, 100 ms and 200 ms), and FIG. 17 shows ethaneconversion and C2 ratio as a function of mole fraction of ethane atvarious residence times (50 ms, 100 ms and 200 ms).

Various approaches can be employed to introduce alkanes to an OCMreactor integrated with a cracking unit. FIGS. 18A-18D show variousapproaches that may be employed. These figures show an OCM reactorcomprising an OCM catalyst unit with a downstream cracking unit, andvarious examples of ethane and propane injection locations. The catalystunit can include a catalyst bed. A hydrocarbon feed (“HC feed”) directsa hydrocarbon (e.g., methane) to the OCM reactor, and an air/O₂ streamdirects air/O₂ to the OCM reactor. The hydrocarbon and air/O₂ streamscan be directed to a pre-conditioning unit of the OCM reactor, such as amixer. Ethane and propane can be provided from an external source, suchas an NGL processing facility and/or as recycle from an OCM productstream. The hydrocarbon, air/O₂, ethane and propane streams can bedirected to heat exchangers to preheat the streams prior to introductionto the OCM reactor. In the figures, lengths L₁, L₂ and L₃ can beselected to optimize ethane and propane cracking to desired or otherwisepredetermined products, which can be a function of gas temperature andresidence time. The ethane injection location is upstream of the propaneinjection location.

During use, the hydrocarbon and air/O₂ directed into the OCM reactorreact to form OCM products that are directed along ahydrocarbon-containing stream to the cracking unit and out of the OCMreactor. In the cracking unit, any alkanes in the hydrocarbon-containingstream, including alkanes introduced to the catalyst unit and/orcracking unit from an external source and any alkanes formed in thecatalyst unit, can be cracked to alkenes and directed out of the OCMreactor along the hydrocarbon-containing stream.

In FIG. 18A, separate ethane and propane injection locations introduceethane and propane to the cracking unit. In FIG. 18B, integral heatexchange is employed to remove heat from catalyst unit and to heat theethane stream prior to introduction of the ethane stream into thecracking unit. As an alternative, ethane can be injected into the bottomof the catalyst unit, as shown in FIG. 18C. In FIG. 18D, ethane andpropane are injected at the same location (or co-injected).

An aspect of the present disclosure provides mixers and methods ofmixing compounds (e.g., ethane and propane) into the cracking unit.Operation of the OCM process with ethane added to the cracking unit canbenefit from conditions whereby; (a) ethane is injected into anduniformly mixed with the OCM exhaust gas, and (b) the mixed gases areprovided sufficient residence time for conversion prior to thermalquenching. Thermal quenching can halt reactions that yield undesirablehydrocarbon constituents at the expense of ethylene. The mixing ofethane and OCM exhaust gas can be accomplished in a process that israpid and results in a uniformly blended mixture.

In some cases, high ethylene yields are obtained by providing forresidence times between ethane injection and thermal quenching of atleast about 5 milliseconds (ms), at least about 10 ms, at least about 20ms, at least about 30 ms, at least about 40 ms, at least about 50 ms, atleast about 60 ms, at least about 70 ms, at least about 80 ms, at leastabout 100 ms, at least about 120 ms, at least about 140 ms, at leastabout 160 ms, at least about 180 ms, at least about 200 ms, at leastabout 300 ms, or at least about 400 ms. In some cases, the residencetime is at most about 5 ms, at most about 10 ms, at most about 20 ms, atmost about 30 ms, at most about 40 ms, at most about 50 ms, at mostabout 60 ms, at most about 70 ms, at most about 80 ms, at most about 100ms, at most about 120 ms, at most about 140 ms, at most about 160 ms, atmost about 180 ms, at most about 200 ms, at most about 300 ms, or atmost about 400 ms. In some cases, the residence time is between about 10ms and 100 ms, between about 30 ms and about 80 ms, or between about 50ms and about 60 ms.

In some embodiments, the alkane (e.g., ethane or propane) is mixed withthe OCM exhaust gas uniformly before exiting the mixer, upon exiting themixer, or prior to initiation of a cracking reaction. The alkane and OCMexhaust gas can be mixed such that the mixed gas has variations intemperature, alkane concentration, or flow rate that do not deviate morethan about 1%, 3%, 5%, 10%, 15%, 20%, 25%, 30%, 50%, 60%, or 80% fromthe average temperature, alkane concentration, or flow rate.

The mixers and mixing processes described herein can result in broadspectrums of mixture ratios. In one embodiment of the mixer, the OCMexhaust gas enters the system at a large end of a converging section inan axial direction. Ethane is injected into the converging sectionthrough a plurality of ports that can be directed to produce ethane jetshaving axial, radial and tangential velocity components. The ports canbe substantially directed in tangential and radial directions. Theconverging section can be connected to a duct of smaller diameter (e.g.,the reactor). The geometry of the converging and reactor sections(diameters and lengths) can be selected to provide the desired residencetimes for reactions to occur. In some cases, a heat exchanger is locateddownstream of and connected to the reactor, which can be utilized tothermally quench the gas stream. The mixer can be made out of materialsthat can withstand high temperatures (e.g., about 800 C to 1000 C, whichcan be the temperature of the OCM exhaust gas). Examples of suitablematerials are ceramics such as alumina.

Post-Bed Cracking

An aspect of the present disclosure provides OCM systems and methods forincreasing the concentration of alkenes (or olefins) in C₂₊ compoundsoutputted from an OCM reactor. An OCM system can provide improved alkeneyield by in situ alkane cracking in a post-bed section of a reactor(post-bed cracking). Such in situ cracking of alkanes can provide aproduct stream with hydrocarbon distributions tailored for various enduses. This can advantageously provide C₂₊ product stream that may bebetter suited for downstream uses, such as the commercial production ofpolymeric materials, as well as greater carbon efficiency of the overallprocess.

Post-bed cracking techniques can comprise control of temperature andresidence time. Temperature and residence time can be chosen to favorhigher ethylene concentration in the effluent from an OCM reactor.Post-bed cracking can be achieved using energy within the OCM effluent.Post-bed cracking can comprise cracking in the presence of OCM effluentsteam. Cracking in the presence of steam, such as OCM effluent steam,can provide a higher C2 ratio.

Post-bed cracking can be conducted with a low residence time in thepost-bed section. The residence time in the post-bed section can be lessthan or equal to about 500 milliseconds (ms), 450 ms, 400 ms, 350 ms,300 ms, 250 ms, 200 ms, 150 ms, 140 ms, 130 ms, 120 ms, 110 ms, 100 ms,90 ms, 80 ms, 70 ms, 60 ms, 50 ms, 40 ms, 30 ms, 20 ms, or 10 ms. Theresidence time in the post-bed section can be about 500 milliseconds(ms), 450 ms, 400 ms, 350 ms, 300 ms, 250 ms, 200 ms, 150 ms, 140 ms,130 ms, 120 ms, 110 ms, 100 ms, 90 ms, 80 ms, 70 ms, 60 ms, 50 ms, 40ms, 30 ms, 20 ms, or 10 ms.

Post-bed cracking can be conducted at a particular temperature or withina particular temperature range. The post-bed cracking temperature can beat least about 600° C., 650° C., 700° C., 720° C., 740° C., 760° C.,780° C., 800° C., 810° C., 820° C., 830° C., 840° C., 850° C., 860° C.,870° C., 880° C., 890° C., 900° C., 910° C., 920° C., 930° C., 940° C.,or 950° C. The post-bed cracking temperature can be at most about 600°C., 650° C., 700° C., 720° C., 740° C., 760° C., 780° C., 800° C., 810°C., 820° C., 830° C., 840° C., 850° C., 860° C., 870° C., 880° C., 890°C., 900° C., 910° C., 920° C., 930° C., 940° C., or 950° C. The post-bedcracking temperature can be about 600° C., 650° C., 700° C., 720° C.,740° C., 760° C., 780° C., 800° C., 810° C., 820° C., 830° C., 840° C.,850° C., 860° C., 870° C., 880° C., 890° C., 900° C., 910° C., 920° C.,930° C., 940° C., or 950° C. The post-bed cracking temperature can befrom about 800° C. to about 950° C. The post-bed cracking temperaturecan be from about 810° C. to about 950° C. The post-bed crackingtemperature can be from about 820° C. to about 950° C. The post-bedcracking temperature can be from about 830° C. to about 950° C. Thepost-bed cracking temperature can be from about 840° C. to about 950° C.The post-bed cracking temperature can be from about 850° C. to about950° C. The post-bed cracking temperature can be from about 860° C. toabout 950° C. The post-bed cracking temperature can be from about 870°C. to about 950° C. The post-bed cracking temperature can be from about880° C. to about 950° C.

The product stream from processes described herein can have particularcompositions. In some cases, the product stream can comprise an acetonecontent less than or equal to about 100 parts-per-million (ppm), 50 ppm,10 ppm, 5 ppm, 1 ppm, 100 parts-per-billion (ppb), 50 ppb, 10 ppb, 5ppb, or 1 ppb. In some cases, the product stream can comprise a carbondioxide (CO₂) content less than or equal to about 100 parts-per-million(ppm), 50 ppm, 10 ppm, 5 ppm, 1 ppm, 100 parts-per-billion (ppb), 50ppb, 10 ppb, 5 ppb, or 1 ppb. In some cases, the product stream cancomprise a carbon monoxide (CO) content less than or equal to about 100parts-per-million (ppm), 50 ppm, 10 ppm, 5 ppm, 1 ppm, 100parts-per-billion (ppb), 50 ppb, 10 ppb, 5 ppb, or 1 ppb. In some cases,the product stream can comprise an acetylene content less than or equalto about 2000 parts-per-million (ppm), 1000 ppm, 900 ppm, 800 ppm, 700ppm, or 600 ppm. In some cases, the product stream can comprise a butenecontent less than or equal to about 200 parts-per-million (ppm) or 100ppm. In some cases, the product stream can comprise a propylene contentthat is greater than or equal to about 0.2%, 0.4%, 0.6%, 0.8%, 1%, %,3%, 4%, 5%, 6%, 7%, 8%, or 9% relative to an ethylene content of theproduct stream.

The post-bed region can be used to crack additional externalhydrocarbons (e.g., ethane, propane) beyond those contained in the OCMeffluent. The heat capacity in the OCM effluent can be sufficient tocrack additional hydrocarbons. External hydrocarbons can be providedfrom a recycle stream. External hydrocarbons can be heated prior toinjection into the post-bed section. External hydrocarbons can be heatedby, for example, heat exchange with the OCM catalyst bed.

External hydrocarbons to be cracked in the post-bed section can be addedsequentially based on carbon number. For example, external hydrocarbonswith a lower carbon number (e.g., ethane) can be added to the post-bedcracking region upstream of where external hydrocarbons with a highercarbon number (e.g., propane) are added to the post-bed cracking region.The temperature in the post-bed cracking region can decrease going fromthe catalyst bed to the reactor outlet. Sequential adding of externalhydrocarbons based on carbon number can be used to contact higher carbonnumber hydrocarbons with lower post-bed cracking temperatures.Sequential addition of external hydrocarbons can result in improvedtotal olefin yields.

The present disclosure provides a reactor system comprising a plug flowreactor with a heat exchanger. The heat exchanger can include one ormore heat exchange coils, such as at least 1, 2, 3, 4, 5, 6, 7, 8, 9,10, 20, 30, 40, 50, or 100 coils. The coils can be part of the samefluid flow path (e.g., tube) or separate fluid flow paths. An OCMreactor can comprise a mixer on top of the reactor to mix a hydrocarbonstream (e.g., natural gas) with an oxygen or air stream. An OCM reactorcan comprise an axial fixed catalytic bed, where a hydrocarbon feedstream exothermically reacts with an oxygen stream. An OCM reactor cancomprise an empty space below the catalytic bed, which can allow controlof residence time to optimize ethane cracking to ethylene (e.g.,post-bed cracking). A reactor can comprise a mixer, an axial fixedcatalytic bed, and a space for post-bed cracking; components can bedesigned to provide a plug-flow flow pattern through the reactor and tocontrol residence times. Reactor outlet can be fed into a heat recoverysteam generator (HRSG) tubesheet. An OCM reactor can comprise a heatexchanger (e.g., heat exchange coils, heat exchange tubes). A heatexchanger can be located before the reactor outlet, such as after apost-bed cracking space and before feeding into an HRSG tubesheet. Aheat exchanger can be used to cool down reactor OCM effluent. A heatexchanger can be used to heat an OCM feed stream. A heat exchanger canbe used to heat saturated steam. A heat exchanger can be used to heatboiler feed water (BFW). A heat exchanger can be used to heat an oxygenor air stream. A heat exchanger can reduce the temperature of an OCMeffluent stream below the temperature range at which cracking reactionscan occur (e.g., below 600° C.). This can reduce or prevent cokeformation, such as coke formation in an HRSG system.

Reactor systems can comprise a low flow pocket with catalytically inertmaterial. FIG. 19 shows a reactor 1901 with an OCM catalyst bed 1902.The low flow pocket can be in at least a portion of the catalyst bed1902 or extend through all or substantially all of the catalyst bed1902, such as at least about 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%,95%, or 99% of the catalyst bed 1902. A region of catalytically inertmaterial 1903 can be included in the catalyst bed. The catalyticallyinert material can include a material that does not facilitate orappreciably facilitate an OCM process. A stream of natural gas andoxygen 1904 can be flowed into the reactor inlet. A stream of otherhydrocarbons (e.g., C2, C3) 1905 can be injected into the inert region.A product stream 1906 of OCM and cracking products can exit the reactor.An inert region can be used to create a low flow pocket. The inertregion can comprise different particle sizes compared to the maincatalyst bed. The inert region can discharge into the post-bed crackingregion. The inert region can result in an increased residence time formaterial injected into the region (e.g., C2 and C3 hydrocarbons).Increased residence time can result in additional heat transfer to theinjected material. Most or all of the oxygen provided to the reactor canbe consumed upstream of the inert region. At least about 50%, 60%, 70%,80%, 90%, 95%, 96%, 97%, 98%, 99%, 99.9%, 99.99%, 99.999%, or 100% ofthe oxygen provided to the reactor can be consumed upstream of the inertregion.

Prior to cracking, alkanes such as ethane or propane can be pre-heated.Alkanes can be pre-heated to a temperature of at least about 500° C.,510° C., 520° C., 530° C., 540° C., 550° C., 560° C., 570° C., 580° C.,590° C., 600° C., 610° C., 620° C., 630° C., 640° C., 650° C., 660° C.,670° C., 680° C., 690° C., 700° C., 710° C., 720° C., 730° C., 740° C.,750° C., 760° C., 770° C., 780° C., 790° C., 800° C., 810° C., 820° C.,830° C., 840° C., 850° C., 860° C., 870° C., 880° C., 890° C., or 900°C. Pre-heating can be conducted in the presence of steam. Steam can beadded as an oxidant. Steam can be added as a diluent. Pre-heating can beconducted in the absence of steam. Pre-heating can be conducted in thepresence of CO₂. CO₂ can be added as an oxidant. CO₂ can be added as adiluent (i.e., a diluting agent). The specific heat capacity of CO₂ isabout 2.5 times lower than that of steam. Mixing hydrocarbons with CO₂rather than with steam can result in a higher mixture temperature. Therate of ethane thermal cracking can be enhanced by the presence of CO₂.Increased concentrations of CO₂ can shift the Boudouard reaction to theleft and mitigate coke production. A system using added CO₂ can comprisea downstream amine scrubber for CO₂ separation.

A hybrid reactor system can be employed which combines isothermal andadiabatic sections. An isothermal section can comprise a tubular reactoras described herein. Process operating conditions, such as inlettemperature, flow rate, and heat transfer medium level, can becontrolled to produce reactor effluent (e.g., OCM reactor effluent) at adesired temperature or composition. A hybrid reactor comprising a firstisothermal tubular stage followed by a second adiabatic stage canprovide high conversion, high ethylene yield, and high C2 ratio.

The present disclosure provides for a reactor system comprising atwo-reactor configuration. A two-reactor system can comprise a first OCMreactor and second cracking reactor. The second cracking reactor cancomprise a smaller diameter or width than the first OCM reactor. Thefirst OCM reactor can comprise a tubular reactor. The second crackingreactor can comprise a tubular reactor. At least about 50%, 60%, 70%,80%, 90%, 95%, 96%, 97%, 98%, 99%, 99.9%, 99.99%, 99.999%, or 100% ofthe oxygen provided to the first OCM reactor can be consumed within thefirst OCM reactor. The outlet stream from the first OCM reactor can befed into the second cracking reactor. The second cracking reactor can beheated. The residence time within the second cracking reactor can besmaller than the residence time within the first OCM reactor by at leastabout 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 3, 4, 5, 6, 7, 8,9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600,700, 800, 900, or 1000 times. Relative residence times can be controlledby designing the relative diameter or width of the two reactors. Thesecond cracking reactor can comprise packing or support material (e.g.SiC rings or spheres). Packing or support material can provideadditional surface area for cracking.

Auto-Thermal Reforming

Systems of the present disclosure may be employed for use inauto-thermal reforming (ATR). In ATR, methane reacts with oxygen andsteam to produce syngas (primarily CO and H₂) with a targeted CO/H₂ratio. An ATR reactor typically includes a burner followed by acatalytic bed containing an ATR catalyst (e.g., nickel). In the burner,combustion is the primary reaction and generates the heat that is thenused in the catalytic bed to feed the reforming reactions. In thecatalytic bed, reactions approach near final chemical equilibrium at asignificantly lower temperature than in the burner zone, which may bethermodynamically favorable and leads to higher conversions.

From a chemical process standpoint, the optimal design for an ATR unitmay be one where both combustion and reforming reactions occursimultaneously over a catalytic bed. Such a design is described as aflame-less ATR, i.e., an ATR without the burner zone. While this designmay lead to higher conversion and reduced consumption of oxygen, itstechnical implementation is only enabled if a suitable mixer exists,such as, for example, a mixer that 1) mixes methane-containing andoxygen-containing streams with the required degree of uniformity priorto entering the catalytic bed for ATR, and 2) mixes themethane-containing and oxygen-containing streams entirely within theauto-ignition delay time. In fact, if only a portion of the mixed streamis allowed to spend longer than the auto-ignition delay time in themixer zone, combustion can start, thus generating a flame that maypropagate through the entire mixture. The catalytic bed would not beable to withstand the flame temperature, leading to a technical failureof the ATR system. Conversely, if the mixer can uniformly combine theentire streams within the maximum allowable time, the un-reacted mixedstream can proceed to the catalytic bed, where methane can be optimallyconverted to syngas. In view of this requirement, the distribution ofresidence times in the mixer can be such that 100% of the mixed streamspends less than the auto-ignition delay time in the mixer itself.

Auto-thermal reforming systems of the present disclosure can includemixers, which can reduce auto-ignition delay times prior to directingmethane and oxygen to an ATR catalyst. In some embodiments, a method forflame-less auto-thermal reforming (ATR) to generate syngas comprisesmixing a first gas stream comprising methane with a second gas streamcomprising oxygen to form a third gas stream, and prior to auto-ignitionof the third gas stream, performing a flame-less ATR reaction using thethird gas stream to produce a product stream comprising hydrogen (H₂)and carbon monoxide (CO).

For example, a mixer for use in ATR can uniformly combine two or moregaseous streams into one gaseous stream while allowing for the mixedstream in its entirety to spend only a maximum allowable time in themixer itself. The mixer can include a series of parallel airfoil-shapedmanifolds inserted in the cross section of a reactor or any other flowdevice, such as a pipe, that carries one of the gaseous streams. Theother gaseous streams are fed to the airfoil-shaped manifolds, whichhave suitably designed ports to enable the injection of the gas insidethe manifolds into the main gaseous stream flowing outside themanifolds.

Computer Control Systems

The present disclosure provides computer control systems that can beemployed to regulate or otherwise control OCM methods and systemsprovided herein. A control system of the present disclosure can beprogrammed to control process parameters to, for example, effect a givenproduct distribution, such as a higher concentration of alkenes ascompared to alkanes in a product stream out of an OCM reactor.

FIG. 20 shows a computer system 2001 that is programmed or otherwiseconfigured to regulate OCM reactions, such as regulate fluid properties(e.g., temperature, pressure and stream flow rate(s)), mixing, heatexchange and OCM reactions. The computer system 2001 can regulate, forexample, fluid stream (“stream”) flow rates, stream temperatures, streampressures, OCM reactor temperature, OCM reactor pressure, the quantityof products that are recycled, and the quantity of a first stream (e.g.,methane stream) that is mixed with a second stream (e.g., air stream).

The computer system 2001 includes a central processing unit (CPU, also“processor” and “computer processor” herein) 2005, which can be a singlecore or multi core processor, or a plurality of processors for parallelprocessing. The computer system 2001 also includes memory or memorylocation 2010 (e.g., random-access memory, read-only memory, flashmemory), electronic storage unit 2015 (e.g., hard disk), communicationinterface 2020 (e.g., network adapter) for communicating with one ormore other systems, and peripheral devices 2025, such as cache, othermemory, data storage and/or electronic display adapters. The memory2010, storage unit 2015, interface 2020 and peripheral devices 2025 arein communication with the CPU 2005 through a communication bus (solidlines), such as a motherboard. The storage unit 2015 can be a datastorage unit (or data repository) for storing data.

The CPU 2005 can execute a sequence of machine-readable instructions,which can be embodied in a program or software. The instructions may bestored in a memory location, such as the memory 2010. Examples ofoperations performed by the CPU 2005 can include fetch, decode, execute,and writeback.

The storage unit 2015 can store files, such as drivers, libraries andsaved programs. The storage unit 2015 can store programs generated byusers and recorded sessions, as well as output(s) associated with theprograms. The storage unit 2015 can store user data, e.g., userpreferences and user programs. The computer system 2001 in some casescan include one or more additional data storage units that are externalto the computer system 2001, such as located on a remote server that isin communication with the computer system 2001 through an intranet orthe Internet.

The computer system 2001 can be in communication with an OCM system2030, including various elements of the OCM system. Such elements caninclude sensors, flow regulators (e.g., valves), and pumping systemsthat are configured to direct a fluid.

Methods as described herein can be implemented by way of machine (e.g.,computer processor) executable code stored on an electronic storagelocation of the computer system 2001, such as, for example, on thememory 2010 or electronic storage unit 2015. The machine executable ormachine readable code can be provided in the form of software. Duringuse, the code can be executed by the processor 2005. In some cases, thecode can be retrieved from the storage unit 2015 and stored on thememory 2010 for ready access by the processor 2005. In some situations,the electronic storage unit 2015 can be precluded, andmachine-executable instructions are stored on memory 2010.

The code can be pre-compiled and configured for use with a machine havea processer adapted to execute the code, or can be compiled duringruntime. The code can be supplied in a programming language that can beselected to enable the code to execute in a pre-compiled or as-compiledfashion.

Aspects of the systems and methods provided herein, such as the computersystem 2001, can be embodied in programming. Various aspects of thetechnology may be thought of as “products” or “articles of manufacture”typically in the form of machine (or processor) executable code and/orassociated data that is carried on or embodied in a type of machinereadable medium. Machine-executable code can be stored on an electronicstorage unit, such memory (e.g., read-only memory, random-access memory,flash memory) or a hard disk. “Storage” type media can include any orall of the tangible memory of the computers, processors or the like, orassociated modules thereof, such as various semiconductor memories, tapedrives, disk drives and the like, which may provide non-transitorystorage at any time for the software programming. All or portions of thesoftware may at times be communicated through the Internet or variousother telecommunication networks. Such communications, for example, mayenable loading of the software from one computer or processor intoanother, for example, from a management server or host computer into thecomputer platform of an application server. Thus, another type of mediathat may bear the software elements includes optical, electrical andelectromagnetic waves, such as used across physical interfaces betweenlocal devices, through wired and optical landline networks and overvarious air-links. The physical elements that carry such waves, such aswired or wireless links, optical links or the like, also may beconsidered as media bearing the software. As used herein, unlessrestricted to non-transitory, tangible “storage” media, terms such ascomputer or machine “readable medium” refer to any medium thatparticipates in providing instructions to a processor for execution.

Hence, a machine readable medium, such as computer-executable code, maytake many forms, including but not limited to, a tangible storagemedium, a carrier wave medium or physical transmission medium.Non-volatile storage media include, for example, optical or magneticdisks, such as any of the storage devices in any computer(s) or thelike, such as may be used to implement the databases, etc. shown in thedrawings. Volatile storage media include dynamic memory, such as mainmemory of such a computer platform. Tangible transmission media includecoaxial cables; copper wire and fiber optics, including the wires thatcomprise a bus within a computer system. Carrier-wave transmission mediamay take the form of electric or electromagnetic signals, or acoustic orlight waves such as those generated during radio frequency (RF) andinfrared (IR) data communications. Common forms of computer-readablemedia therefore include for example: a floppy disk, a flexible disk,hard disk, magnetic tape, any other magnetic medium, a CD-ROM, DVD orDVD-ROM, any other optical medium, punch cards paper tape, any otherphysical storage medium with patterns of holes, a RAM, a ROM, a PROM andEPROM, a FLASH-EPROM, any other memory chip or cartridge, a carrier wavetransporting data or instructions, cables or links transporting such acarrier wave, or any other medium from which a computer may readprogramming code and/or data. Many of these forms of computer readablemedia may be involved in carrying one or more sequences of one or moreinstructions to a processor for execution.

Although systems and methods of the present disclosure have beendescribed in the context of methane and air (or oxygen), such systemsand methods may be employed for use with other hydrocarbons andoxidizing agents (e.g., NO₃, NO₂, or O₃). Non-limiting examples ofhydrocarbons include alkanes, alkenes, alkynes, aldehydes, ketones, andcombinations thereof. For instance, mixers and integrated heat exchangesof the disclosure may be employed for use with ethane, propane, pentane,or hexane. Non-limiting examples of oxidizing agents include O₂, H₂O₂,NO₃, NO₂, O₃, and combinations thereof. Moreover, although certainexamples of the present disclosure have made reference to air, otherfluids containing oxygen or an oxidizing agent (e.g., NO₂) may be used.

EXAMPLES Example 1—Post-Bed Cracking of Ethane

A reactor system is provided comprising an OCM reactor with an OCMcatalyst bed section and a post-bed cracking section. The ratio ofmethane and oxygen provided to the OCM catalyst bed section is adjustedto control the temperature of the stream at the outlet of the OCMcatalyst bed section leading into the post-bed cracking section. Thetemperature is between about 880° C. and about 900° C. Results are shownin FIG. 21 for percent ethylene in post-bed cracking section effluentversus percent ethane in post-bed cracking section inlet stream (uppergraph), for C₂H₄ selectivity versus percent ethane in post-bed crackingsection inlet stream (middle graph), and for ethane conversion versuspercent ethane in post-bed cracking section inlet stream (lower graph).

Example 2—Flow Splitting Reactor

An example of a reactor having a flow split of the OCM feed gas is shownin FIG. 22. Here, the OCM gas feed mixture 2200 containing both naturalgas and oxygen is first split into two streams. A first stream 2205 isthen reacted in a first OCM reactor 2210 before having its effluentrecombined with the second stream 2215. The combined stream is thenreacted further in a second OCM reactor 2220 or catalyzed reactorsection to produce a product 2225. The first and/or second OCM reactorscan have a mixer or mixing region 2230. In some cases the first andsecond OCM reactors are regions of a single OCM reactor.

The ratio of gas flow directed to the first reactor to the total feedflow in the system can be between about 5% and about 50%, or in somecases between about 10% and about 35%. The feed inlet temperature can bebetween about 400° C. and about 550° C. with an amount of oxygen in thefeed as needed to achieve a system outlet temperature (or adiabatictemperature of the product mixture) of between about 820° C. and about920° C.

For an adiabatic system, the inlet temperature of a well-mixed stream atthe inlet to the second OCM 2220 can be adjusted to be between about500° C. and about 750° C. or between about 600° C. and about 700° C. bychoosing the proper ratio of the flow of the first stream 2205 to thesecond stream 2215.

The extent of mixing in the second OCM reactor 2220 can be adjusted toavoid or create non axial (in flow direction) temperature and oxygenconcentration gradients. There can be instances where these gradientsare desirable to improve system operability (e.g., for operation belowlight off inlet temperature of the catalyst and above extinctiontemperature of the catalyst of reactor). In some cases, hot spots at thefront end of the second reactor 2220 reactor can promote catalystactivity at the front end of the catalyst bed.

Example 3—Flow Splitting Reactor

Another example of a reactor having OCM flow split is shown in FIG. 23.In this design, a first OCM reactor 2300, one or more bypass legs 2305and the second OCM reactor 2310 are contained within the same reactorshell. Flow splitting and bypass of the OCM feed gas is obtained byimbedding catalytically inert tubes within the catalyst packing toprovide pathways for the feed gas through the first reactor section 2300that is free of contact from catalytically active surfaces. A mixingregion 2315 can be provided between the first and second OCM reactorsections.

The reactor system was assembled according to the schematic shown inFIG. 23. The catalyst shape was 3 mm extrudate cut into about 1 cmlengths. The refractory lined container internal diameter (ID) was 2.2inches. The first OCM reactor section was 3 inches long with three 10 mmID quartz tubes set to bypass about 70% of the inlet feed to the secondreactor section.

One inch of Zirconia beads (3 mm diameter) were used in the mixer region2315 to mix the bypass flow and the reactor streams from the firstreactor section.

The second reactor section 2310 also used a 3 inches long OCM catalystbed made of the same catalyst material as the first reactor section.

The gas linear velocity through the OCM catalyst packing in the firstsection was about 35% of the gas linear velocity through the OCMcatalyst packing in the second section. The contact time of the reactingfeed to the catalyst is about 3-fold greater in the first OCM reactorsection 2300 than in the second OCM reactor section 2310.

Example 4—Separate Reaction of Wet and Dry Natural Gas

The flow splitting reactors and methods described herein can also beused for different gas feeds being processed in different reactors orreactor subsections. A potential benefit of such an implementation canbe that processing of wet natural gas feed (e.g., containing above 2%C₂₊ hydrocarbons) in the second OCM reactor can be more effective thanprocessing this mixture through a single packed bed reactor.

With reference to FIG. 24, when both dry and wet natural gas feeds areavailable (e.g., when using a pressure swing adsorption system to drypart of the natural gas coming into the plant), it can advantageous touse the dry natural gas feed 2400 to provide heat and product throughthe first OCM reactor section 2405, while the wet natural gas feed 2410can be directed to the second OCM reactor section 2415 to minimizecombustion of the C₂₊ molecules contained in the wet gas feed. Thehydrocarbon to oxygen ratio and pre-heating temperature of the two feedstreams can be controlled independently.

In some cases, integration within a single shell can be desirable (e.g.,to minimize heat losses and residence time of the unreactive feed priorto contact the catalytic material). FIG. 25 shows an embodiment of suchsystem with separate feeds. A first feed 2500 is directed into a firstreactor or reactor segment 2505 and a second feed 2510 is directed intoa second reactor or reactor segment 2515. The feeds can differ in anynumber of ways including by their natural gas to oxygen ratio, by theirtemperature of pre-heating, or being for wet and dry natural gas.

This embodiment can allow external control of the split ratio of bypassgas to total gas (in contrast to a system relying on pressure dropdefined by the catalyst bed packing flow resistance to set the splitratios).

Example 5—Flow Splitting Reaction

The reactor system assembled in Example 3 was tested for OCM catalyticperformance when used as the second reactor in a series of OCM reactors.The reactor system inlet contained a mixture of methane, ethylene,ethane, CO, CO₂, water and hydrogen, to which air was added.

Performance of the reactor system with bypass tubes was compared to theperformance of the same catalyst (and amount thereof) without flowsplitting and staged reaction of the oxygen. FIG. 26 compares thedifferential selectivity as a function of peak bed temperature for thesystem with a bypass reactor 2600 and without a bypass reactor 2605.Differential (net) selectivity to higher hydrocarbons (ethylene, ethane,propane and propylene) was measured as a function of the amount ofoxygen injected, resulting in different adiabatic operating temperaturesfor the reactor back end. The data points shown are for a reactor systeminlet temperature of 515° C.

This example shows the benefit with regard to selectivity of the stagingof oxygen consumption in different reactor sub-sections for theselective coupling of methane of feed gas containing highly reactivespecies.

FIG. 27 shows performance versus the reactor system inlet feedtemperature. Here, the single packed bed performance quickly drops withinlet temperature 2700, whereas the split flow system with staged oxygenconsumption is still operational down to about 460° C. 2710. Oxygenbreakthrough analysis also shows the same trend (data now shown).

Example 6—Reactor with Heat Exchange

The reactors with heat exchange described herein can be used to removeor inject heat into a catalyst bed carrying out an exothermic orendothermic chemical reaction. FIG. 28 presents a schematic drawing of atypical reactor with heat exchange. The catalyst bed 2800 is loaded innarrow and long tubes assembled into an area of the reactor that hasfeed gas flowing into the reactor 2805 and product gas flowing out ofthe reactor 2810. The outer side of the tube is contacted with a heattransfer media that enters 2815 and exits 2820 the reactor, but does notdirectly contact the catalyst bed. Molten salt are the preferred heattransfer media for temperatures above about 400° C. and below about 600°C.

As OCM can be performed at temperature as low as 420° C. (e.g., usingcatalyst described in U.S. patent application Ser. No. 13/115,082, U.S.patent application Ser. No. 13/479,767, U.S. patent application Ser. No.13/689,611, and U.S. patent application Ser. No. 13/901,319, each ofwhich is incorporated herein by reference in its entirety), the moltensalt cooled tubular reactors described herein can be used to build areactor system with increased ethylene yield compared to adiabatic typereactors. Additional description of performing OCM in reactors with heatexchange can be found in U.S. patent application Ser. No. 13/900,898,which is incorporated herein by reference in its entirety.

Demonstration of the benefit of this type of reactor was carried out apilot scale using 5 feet long single tube reactors. In the followingexamples, different catalyst packing strategies enhanced the reactorperformance or operability as described.

Example 7—Molten Salt OCM Tubular Reactor

A one-inch section of schedule 40 pipe (1.05 inches ID) made of 304stainless steel was welded to a U tube. A packed bed of 14 inches of OCMcatalyst having ring shaped particles of 6 mm OD and 3 mm ID was loadedin the tube. The reactor tube was immersed in a HITEC heat transfer saltbath with a molten level above the exit of the catalyst bed packing. Themolten salt was circulated to insure good temperature uniformity of themolten salt bath.

Feed gas coming into the bottom of the 1-inch pipe through the U tubewas pre-heated by the hot molten salt before contacting the OCM catalystin the pipe.

The molten salt temperature was controlled between 450° C. and 550° C.External wall temperature of the pipe was measured every 3 inches andthe catalyst operating conditions were adjusted to keep the outer pipewall temperature under 600° C.

Methane and air mixtures were fed through the reactor at total gas flowrate between 50 and 100 SLPM (standard liter per minute) and a pressurebetween 1 and 2 bar-gauge (barg). The ratio of methane to oxygen wasvaried between 4 and 10.

Example 8—Effect of Bed Packing

The reactor described in Example 7 was packed with a catalyst packingdivided into two sections. A first section (3 inches long) was separatedfrom a second section (11 inches long) section by 2 inches of siliconcarbide bead packing (6 mm diameter). The silicon carbide is chemicallyinert and does not activate methane or oxygen. However, this inactivematerial allows for cooling of the partially reacted process stream,resulting in a significant change in the axial temperature profile ofthe reactor.

FIG. 30 shows a graph of C₂₊ selectivity of the OCM reaction versusmethane conversion. The un-segmented catalyst bed (14-inch) described inExample 7 is shown as square markers 3000 and the segmented catalyst bed(3-inch and 14-inch sections) is shown as diamond markers 3010. Thecomparison of the two bed packing geometries was performed at about 1.5barg and a total feed flow of 50 SLPM with a molten salt temperature of550° C.

FIG. 30 shows that the segmented catalyst bed has an improved C₂₊selectivity. This difference is also reflected in the thermal profile ofthe catalyst with a decreased peak temperature for the segmented bedversus the non-segmented bed (data not shown). While the reactor walltemperature is maintained below 600° C., the center of the tube canreach temperature in excess of 900° C. A stable axial and radialtemperature profile was observed in the catalyst bed. As hot catalystspots above 900° C. can be detrimental to the selectivity of the OCMreaction, addition of axial cooling bands can affect the operatingwindow and performance of the tubular molten salt cooled reactor.

Example 9—OCM with Low Linear Flow Velocity

The reactor shown in FIG. 31 was used to perform OCM at a low linear gasvelocity. The reactor is a quartz reactor with 22 mm ID and 24 mm OD.External surface of the quartz reactor (the catalyst bed section) wasdensely covered by layers of insulation in order to minimize heat lossfrom the catalyst bed. The standard reaction (i.e., non-low linearvelocity) was performed using 8 mm quartz tubing. The quartz tubing wasinside stainless steel tubing for the quartz tubing housing.

The OCM catalyst was an extrudate that was used for both regular (i.e.,non-low linear velocity run) and low linear velocity trials. Theextrudate was approximately 2 mm in diameter and length. The catalystbed height in the quartz reactor was 5 mm. As shown in FIG. 31, thecatalyst bed was sandwiched by inert ceramic wool layers for flowuniformity and minimization of radiation heat transfer.

The flow rates employed in the low linear velocity trials are listed inthe table below.

8 mm, Regular 22 mm, Low Linear Reactor Velocity Velocity I.D. (mm) 8 2222 Cross-sectional area (cm2) 0.5 3.8 3.8 Bed height (cm) 2.0 0.5 0.5CH4 flow (SCCM) 400 600 900 Air flow (SCCM; for 190.5 285.7 428.6 CH4/O2= 10) Feed flow (SCCM) 590.5 885.7 1328.6 Linear velocity (cm/min) 796.2157.9 236.9 GHSV (1/hour) 35,259 27,974 41,962

The furnace temperature was raised slowly (ramping rate 2° C./min) forlow linear velocity runs. The steady state performance was measured whenthe furnace temperature reached the target temperatures (500° C., 550°C., 600° C., 650° C. and 700° C., respectively). The feed mixturepreheating temperature reading (measured on top of the inert ceramicwool layer) was slightly lower than furnace temperature, but withinabout 10° C. For regular runs (non-low linear velocity runs), thefurnace ramping temperature was 3° C./min and the furnace temperaturewas used for the preheating temperature.

The C2 selectivity (% ethlyene+ethane) is plotted versus temperature inFIG. 32. The results show that low linear velocity (600 SCCM 3200 or 900SCCM 3205) can have a higher selectivity than high linear velocity (8 mmreactor 3210). Comparing the performance of the low L/D aspect ratiocatalyst bed to a higher L/D aspect ratio for C2 selectivity shows animproved selectivity for the thinner bed operated with low feed gaslinear velocity. C2 Selectivity at 550° C. gas inlet temperatureincreases from about 25% to about 65% by changing the geometry of thecatalyst container, which can illustrate the influence of the thermalprofile within the catalyst bed on OCM reaction product distribution.Another benefit of a low linear velocity can be the ability to usesmaller catalyst particulates in the bed, as flow resistance typicallyscales with linear velocity.

Some low linear velocity reactors include a radial reactor design inwhich the catalyst bed entrance area is maximized relative to a standardaxial reactor geometry as described in U.S. patent application Ser. No.13/900,898, which is incorporated herein by reference in its entirety.

Example 10—Design of an Alkane Mixer

In some embodiments of the present disclosure, alkanes (e.g., ethane) isinjected into the OCM reactor to be converted into ethylene using theheat of the OCM reaction. FIG. 35 shows an example of a mixer that canbe used for alkane injection into the OCM reactor. The mixer is shownfrom a side profile view 3500, from an end view 3505 and from aperspective view 3510. The OCM product gas flows through the center ofthe mixer along its long axis (and optionally around the outside of themixer) 3515. The alkane stream is injected into the mixer in a pluralitydirections perpendicular to the long axis 3520 and mixes with the OCMeffluent as it travels down the center of the mixer along its long axis.FIG. 36 shows an example of a computational fluid dynamics (CFD)simulation of the mixing of the alkane with the OCM product gas.

Additional descriptions of OCM reactors, catalysts and processes thatmay be employed for use with devices, systems and methods of the presentdisclosure may be found in, for example, U.S. patent application Ser.No. 13/900,898, U.S. patent application Ser. No. 13/936,783, U.S. patentapplication Ser. No. 14/099,614, U.S. patent application Ser. No.13/115,082, U.S. patent application Ser. No. 13/479,767, U.S. patentapplication Ser. No. 13/689,611, U.S. patent application Ser. No.13/739,954, U.S. patent application Ser. No. 13/901,319, U.S. patentapplication Ser. No. 14/212,435, U.S. Provisional Patent Application62/050,729, U.S. Provisional Patent Application 62/073,478, and U.S.Provisional Patent Application 62/051,779, each of which is incorporatedherein by reference in its entirety.

It should be understood from the foregoing that, while particularimplementations have been illustrated and described, variousmodifications can be made thereto and are contemplated herein. It isalso not intended that the invention be limited by the specific examplesprovided within the specification. While the invention has beendescribed with reference to the aforementioned specification, thedescriptions and illustrations of the preferable embodiments herein arenot meant to be construed in a limiting sense. Furthermore, it shall beunderstood that all aspects of the invention are not limited to thespecific depictions, configurations or relative proportions set forthherein which depend upon a variety of conditions and variables. Variousmodifications in form and detail of the embodiments of the inventionwill be apparent to a person skilled in the art. It is thereforecontemplated that the invention shall also cover any such modifications,variations and equivalents. It is intended that the following claimsdefine the scope of the invention and that methods and structures withinthe scope of these claims and their equivalents be covered thereby.

What is claimed is:
 1. A system for mixing two or more gas streams, comprising: (a) a conduit comprising a fluid flow path for a first gas; (b) a first gas distribution manifold comprising one or more openings that are distributed across said fluid flow path, wherein said first gas distribution manifold directs a second gas stream into said fluid flow path; (c) a second gas distribution manifold comprising airfoil shaped manifolds that facilitate mixing such that said first gas and said second gas become uniformly mixed; and (d) a reactor bed in fluid communication with said fluid flow path, wherein said reactor bed comprises an oxidative coupling of methane catalyst.
 2. The system of claim 1, wherein said first manifold and second manifold prevent flow separation within said mixer.
 3. The system of claim 1, wherein said manifolds mix said first gas and said second gas within about 200 milliseconds.
 4. The system of claim 1, wherein said reactor bed is in contact with at least a portion of said manifolds.
 5. The system of claim 1, wherein each of said airfoil-shaped manifolds comprises a first end and a second end situated along said fluid flow path, wherein said one or more openings are disposed between said first end and said second end.
 6. A reactor system for performing oxidative coupling of methane to generate hydrocarbon compounds containing at least two carbon atoms (C2₊ compounds), comprising: (a) a mixer comprising (i) a conduit providing a fluid flow path for a first gas stream comprising methane and (ii) a plurality of airfoil-shaped manifolds distributed across said fluid flow path, wherein said airfoil-shaped manifolds inject a second gas stream comprising oxygen into said fluid flow path to provide a third gas stream comprising methane and oxygen; and (b) a catalyst that performs an oxidative coupling of methane (OCM) reaction using said third gas stream to produce a product stream comprising one or more C2₊ compounds.
 7. The reactor system of claim 6, wherein said airfoil-shaped manifolds are in contact with said catalyst.
 8. The reactor system of claim 6, wherein said reactor comprises at least two stages of mixer and catalyst.
 9. The reactor systems of claim 8, wherein said reactor comprises a bypass leg directing a portion of said first gas stream to a mixer stage located after a first catalyst stage and before a second catalyst stage.
 10. The reactor system of claim 6, wherein said reactor comprises an internal heat exchanger that is capable of transferring heat from said catalyst to said second gas stream prior to said second gas stream entering said mixer.
 11. The reactor system of claim 6, wherein said airfoil-shaped manifolds uniformly mix said first and second gas streams to provide said third gas stream.
 12. The reactor system of claim 6, wherein said catalyst is included in a catalyst bed.
 13. The reactor system of claim 12, wherein at least a portion of said catalyst bed is in said mixer.
 14. The reactor system of claim 12, wherein said catalyst bed is in a reactor downstream of said mixer.
 15. A reactor system for performing oxidative coupling of methane to generate hydrocarbon compounds containing at least two carbon atoms (C₂ ₊ compounds), comprising: (a) a mixer capable of mixing a first gas stream comprising methane with a second gas stream comprising oxygen to provide a third gas stream; (b) a catalyst that performs an oxidative coupling of methane (OCM) reaction using said third gas stream to produce a product stream comprising one or more C2+compounds, wherein said OCM reaction liberates heat; and (c) one or more flow reversal pipes in fluid communication with said mixer and at least partially surrounded by said catalyst, wherein said flow reversal pipes comprise an inner pipe circumscribed by an outer pipe along at least a portion of said length of said inner pipe, wherein said inner pipe is open at both ends and said outer pipe is closed at an end that is surrounded by said catalyst, wherein said flow reversal pipes are configured to transfer heat from said catalyst to said second gas stream during flow along said inner pipe and/or a space between said inner pipe and outer pipe.
 16. The reactor of claim 15, wherein said second gas stream (i) flows through said inner pipe into said catalyst along a first direction and (ii) flows in a space between said inner pipe and outer pipe out of said catalyst along a second direction that is substantially opposite to said first direction.
 17. The reactor of claim 15, wherein said second gas stream (i) flows through a space between said inner pipe and outer pipe and into said catalyst along a first direction and (ii) flows in said inner pipe and out of said catalyst along a second direction that is substantially opposite to said first direction.
 18. A system for performing oxidative coupling of methane (OCM) reaction to generate hydrocarbon compounds containing at least two carbon atoms (C2₊ compounds), comprising: (a) an OCM reactor comprising an OCM catalyst that facilitates an OCM reaction to generate said C₂₊ compounds; (b) an injector comprising a fluid flow conduit that directs a first gas stream through at least a portion of said OCM reactor to one or more openings that are in fluid communication with said OCM reactor, wherein said fluid flow conduit is in thermal communication with said OCM reactor, and wherein said first gas stream comprises one of methane and an oxidizing agent; and (c) a gas distribution manifold comprising one or more openings that are in fluid communication with said one or more openings of said injector and said OCM reactor, wherein said gas distribution manifold directs a second gas stream into said OCM reactor, which second gas stream comprises said other of methane and said oxidizing agent.
 19. The system of claim 18, wherein said injector comprises one or more ribs each comprising one or more openings.
 20. The system of claim 19, wherein said one or more ribs are airfoils. 